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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 30, 2018	Jan. 27, 2019	Jul. 01, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	PBPB
Entity Registrant Name	POTBELLY CORPORATION
Entity Central Index Key	0001195734
Current Fiscal Year End Date	--12-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		24,144,586
Entity Public Float			$ 322.0

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 19,775	$ 25,530
Accounts receivable, net of allowances of $113 and $129 as of December 30, 2018 and December 31, 2017, respectively	4,737	5,087
Inventories	3,482	3,525
Prepaid expenses and other current assets	11,426	11,061
Total current assets	39,420	45,203
Property and equipment, net	87,782	103,859
Indefinite-lived intangible assets	3,404	3,404
Goodwill	2,222	2,222
Deferred income taxes, non-current	13,385	11,202
Deferred expenses, net and other assets	7,002	4,840
Total assets	153,215	170,730
Current liabilities
Accounts payable	3,835	3,903
Accrued expenses	25,029	23,273
Accrued income taxes	162	176
Total current liabilities	29,026	27,352
Deferred rent and landlord allowances	22,905	22,987
Other long-term liabilities	5,751	3,153
Total liabilities	57,682	53,492
Stockholders’ equity
Common stock, $0.01 par value—authorized 200,000,000 shares; outstanding 24,142,586 and 24,999,688 shares as of December 30, 2018 and December 31, 2017, respectively	330	318
Additional paid-in-capital	432,771	421,657
Treasury stock, held at cost, 8,801,154 and 6,831,508 shares as of December 30, 2018, and December 31, 2017, respectively	(108,372)	(85,262)
Accumulated deficit	(229,558)	(219,990)
Total stockholders’ equity	95,171	116,723
Non-controlling interest	362	515
Total stockholders' equity	95,533	117,238
Total liabilities and equity	$ 153,215	$ 170,730

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Allowances on accounts receivable	$ 113	$ 129
Common stock, par value	$ 0.01	$ 0.01
Common stock, authorized	200,000,000	200,000,000
Common stock, outstanding	24,142,586	24,999,688
Treasury stock, shares	8,801,154	6,831,508

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Revenues
Total revenues	$ 422,638	$ 428,111	$ 407,131
Sandwich shop operating expenses
Cost of goods sold, excluding depreciation	111,083	113,426	111,026
Labor and related expenses	127,962	126,337	117,838
Occupancy expenses	59,789	58,562	52,444
Other operating expenses	50,363	49,209	43,738
General and administrative expenses	46,862	44,618	40,411
Depreciation expense	23,142	25,680	22,734
Pre-opening costs	472	1,441	1,786
Impairment and loss on disposal of property and equipment	13,567	10,761	4,141
Total expenses	433,240	430,034	394,118
Income (loss) from operations	(10,602)	(1,923)	13,013
Interest expense	142	124	134
Income (loss) before income taxes	(10,744)	(2,047)	12,879
Income tax expense (benefit)	(2,195)	4,643	4,443
Net income (loss)	(8,549)	(6,690)	8,436
Net income attributable to non-controlling interest	329	266	224
Net income (loss) attributable to Potbelly Corporation	$ (8,878)	$ (6,956)	$ 8,212
Net income (loss) per common share attributable to common stockholders:
Basic	$ (0.35)	$ (0.28)	$ 0.32
Diluted	$ (0.35)	$ (0.28)	$ 0.31
Weighted average shares outstanding:
Basic	25,173,171	25,045,427	25,623,809
Diluted	25,173,171	25,045,427	26,231,367
Product [Member]
Revenues
Total revenues	$ 419,426	$ 424,932	$ 404,874
Franchise Royalties And Fees [Member]
Revenues
Total revenues	$ 3,212	$ 3,179	$ 2,257

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Warrants [Member]	Additional Paid-in-Capital [Member]	Accumulated Deficit [Member]	Non-Controlling Interest [Member]
Beginning balance at Dec. 27, 2015	$ 130,213	$ 303	$ (50,000)	$ 909	$ 399,458	$ (221,246)	$ 789
Beginning balance, common shares at Dec. 27, 2015		26,304,261
Net income (loss)	8,436					8,212	224
Stock-based compensation plans	$ 5,776	$ 6			5,770
Stock-based compensation plans, shares		554,368
Exercise of stock warrants, shares	536,000
Excess tax benefits associated with exercise of stock options	$ (663)				(663)
Repurchases of common stock	(22,321)		(22,321)
Repurchases of common stock, shares		(1,719,502)
Distributions to non-controlling interest	(413)						(413)
Contributions from non-controlling interest	151						151
Amortization of stock-based compensation	3,057				3,057
Ending balance at Dec. 25, 2016	124,236	$ 309	(72,321)	909	407,622	(213,034)	751
Ending balance, common shares at Dec. 25, 2016		25,139,127
Net income (loss)	(6,690)					(6,956)	266
Stock-based compensation plans	6,487	$ 7			6,480
Stock-based compensation plans, shares		696,953
Exercise of stock warrants	$ 1,972	$ 2		$ (909)	2,879
Exercise of stock warrants, shares	653,000	241,704
Repurchases of common stock	$ (12,941)		(12,941)
Repurchases of common stock, shares		(1,078,096)
Distributions to non-controlling interest	(513)						(513)
Contributions from non-controlling interest	11						11
Amortization of stock-based compensation	4,676				4,676
Ending balance at Dec. 31, 2017	$ 117,238	$ 318	(85,262)		421,657	(219,990)	515
Ending balance, common shares at Dec. 31, 2017	24,999,688	24,999,688
Net income (loss)	$ (8,549)					(8,878)	329
Cumulative impact of Topic 606 at 1/1/2018	(690)					(690)
Stock-based compensation plans	$ 8,244	$ 12			8,232
Stock-based compensation plans, shares		1,112,544
Exercise of stock warrants, shares	993,000
Repurchases of common stock	$ (22,916)		(22,916)
Repurchases of common stock, shares		(1,953,245)
Distributions to non-controlling interest	(580)						(580)
Contributions from non-controlling interest	98						98
Treasury shares used for stock-based plans	(194)		(194)
Treasury shares used for stock-based plans, shares		(16,401)
Amortization of stock-based compensation	2,882				2,882
Ending balance at Dec. 30, 2018	$ 95,533	$ 330	$ (108,372)		$ 432,771	$ (229,558)	$ 362
Ending balance, common shares at Dec. 30, 2018	24,142,586	24,142,586

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Cash flows from operating activities:
Net income (loss)	$ (8,549)	$ (6,690)	$ 8,436
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	23,142	25,680	22,734
Deferred income tax	(3,016)	6,096	(1,659)
Deferred rent and landlord allowances	(82)	1,911	3,256
Amortization of stock-based compensation	2,882	4,676	3,057
Excess tax deficiency (benefit) from stock-based compensation	1,089	2,112	(31)
Asset impairment, store closure and disposal of property and equipment	13,762	10,947	4,243
Amortization of debt issuance costs	37	37	34
Changes in operating assets and liabilities:
Accounts receivable, net	100	(650)	674
Inventories	43	(160)	(188)
Prepaid expenses and other assets	(694)	(3,190)	3,204
Accounts payable	177	286	(1,899)
Accrued and other liabilities	2,097	764	4,108
Net cash provided by operating activities	30,988	41,819	45,969
Cash flows from investing activities:
Acquisition of franchise shop			(1,108)
Purchases of property and equipment	(21,395)	(34,684)	(36,712)
Net cash used in investing activities	(21,395)	(34,684)	(37,820)
Cash flows from financing activities:
Proceeds from exercise of stock options	8,244	6,487	5,776
Proceeds from exercise of stock warrants		1,972
Excess tax benefit from stock-based compensation			31
Employee taxes on certain stock-based payment arrangements	(194)
Treasury stock repurchase	(22,916)	(12,941)	(22,321)
Contributions from non-controlling interest	98	11	151
Distributions to non-controlling interest	(580)	(513)	(413)
Net cash used in financing activities	(15,348)	(4,984)	(16,776)
Net increase (decrease) in cash and cash equivalents	(5,755)	2,151	(8,627)
Cash and cash equivalents at beginning of period	25,530	23,379	32,006
Cash and cash equivalents at end of period	19,775	25,530	23,379
Supplemental cash flow information:
Income taxes paid	250	1,656	3,663
Interest paid	110	94	108
Supplemental non-cash investing and financing activities:
Unpaid liability for purchases of property and equipment	$ 751	$ 1,741	$ 2,727

Organization and Other Matters

12 Months Ended

Dec. 30, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Other Matters

(1) Organization and Other Matters

Business

Potbelly Corporation (the “Company” or “Potbelly”), through its wholly owned subsidiaries, owns or operates more than 400 company-owned shops in the United States. Additionally, Potbelly franchisees operate approximately 50 shops domestically, and international shops in the Middle East, Canada and India.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

(2) Summary of Significant Accounting Policies

(a) Principles of Consolidation

The consolidated financial statements include the accounts of Potbelly Corporation; its wholly owned subsidiary, Potbelly Illinois, Inc. (“PII”); PII’s wholly owned subsidiaries, Potbelly Franchising, LLC and Potbelly Sandwich Works LLC (“LLC”); eight of LLC’s wholly owned subsidiaries and LLC’s six joint ventures, collectively, the “Company.” All intercompany balances and transactions have been eliminated in consolidation. For consolidated joint ventures, non-controlling interest represents a non-controlling partner’s share of the assets, liabilities and operations related to the seven joint venture investments. The Company has ownership interests ranging from 51-80% in these consolidated joint ventures.

The Company does not have any components of other comprehensive income (loss) recorded within its consolidated financial statements, and, therefore, does not separately present a statement of comprehensive income (loss) in its consolidated financial statements.

(b) Reporting Period

The Company uses a 52/53-week fiscal year that ends on the last Sunday of the calendar year. Approximately every five or six years a 53rd week is added. Fiscal years 2018, 2017 and 2016 consisted of 52, 53 and 52 weeks, respectively.

The Company owns and operates Potbelly Sandwich Shops concepts in the United States. The Company also has domestic and international franchise operations of Potbelly Sandwich Shops concepts. The Company’s chief operating decision maker (the “CODM”) is its Chief Executive Officer. As the CODM reviews financial performance and allocates resources at a consolidated level on a recurring basis, the Company has one operating segment and one reportable segment.

(d) Use of Estimates

The preparation of financial statements in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Significant estimates include amounts for long-lived assets and income taxes. Actual results could differ from those estimates.

(e) Fair Value Measurements

The Company applies fair value accounting for all financial assets and liabilities and nonfinancial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities that are required to be recorded at fair value, the Company assumes the highest and best use of the asset by market participants in which the Company would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as inherent risk, transfer restrictions, and credit risk.

The Company applies the following fair value hierarchy, which prioritizes the inputs used to measure fair value into three levels, and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement:

•

Level 1 — Quoted prices in active markets for identical assets or liabilities.

•

Level 2 — Observable inputs other than quoted prices in active markets for identical assets or liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

•

Level 3 — Inputs that are both unobservable and significant to the overall fair value measurement reflect an entity’s estimates of assumptions that market participants would use in pricing the asset or liability.

(f) Financial Instruments

The Company records all financial instruments at cost, which is the fair value at the date of transaction. The amounts reported in the consolidated balance sheets for cash and cash equivalents, accounts receivable, accounts payable and all other current liabilities approximate their fair value because of the short-term maturities of these instruments.

(g) Cash and Cash Equivalents

The Company considers all highly liquid investment instruments with an original maturity of three months or less when purchased to be cash equivalents. The Company maintains its cash in bank deposit accounts that, at times, may exceed federally insured limits; however, the Company has not experienced any losses in these accounts. The Company believes it is not exposed to any significant credit risk. These are valued within the fair value hierarchy as Level 1 measurements.

(h) Accounts Receivable, net

Accounts receivable, net consists of credit card receivables, amounts owed from vendors and miscellaneous receivables. The Company had credit card receivables of $2.0 million and $1.9 million as of December 30, 2018 and December 31, 2017, respectively.

(i) Inventories

Inventories, which consist of food products, paper goods and supplies, and promotional items, are valued at the lower of cost (first-in, first-out) or market. No adjustment is deemed necessary to reduce inventory to the lower of cost or market value due to the rapid turnover and high utilization of inventory.

(j) Property and Equipment

Property and equipment acquired is recorded at cost less accumulated depreciation. Property and equipment is depreciated based on the straight-line method over the estimated useful lives, generally ranging from three to five years for furniture and fixtures, computer equipment, computer software, and machinery and equipment. Leasehold improvements are depreciated over the shorter of their estimated useful lives or the related lease life, generally 10 to 15 years. For leases with renewal periods at the Company’s option, the Company determines the expected lease period based on whether the renewal of any options are reasonably assured at the inception of the lease.

Direct costs and expenditures for refurbishments and improvements that significantly add to the productive capacity or extend the useful life of an asset are capitalized, whereas the costs of repairs and maintenance are expensed when incurred. Capitalized costs are recorded as part of the asset to which they relate, primarily to leasehold improvements, and such costs are amortized over the asset’s useful life. When assets are retired or sold, the asset cost and related accumulated depreciation are removed from the consolidated balance sheet and any gain or loss is recorded in the consolidated statement of operations.

The Company assesses potential impairments to its long-lived assets, which includes property and equipment, on a quarterly basis or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. Shop-level assets are grouped at the individual shop-level for the purpose of the impairment assessment. Recoverability of an asset is measured by a comparison of the carrying amount of an asset to its estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of the asset group exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset exceeds the fair value of the asset. The fair value of the shop assets is determined using the discounted future cash flow method of anticipated cash flows through the shop’s lease-end date using fair value measurement inputs classified as Level 3. Level 3 inputs are derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. The Company used a weighted average cost of capital to discount the future cash flows. After performing periodic reviews of the company-operated shops during each quarter of 2018, 2017 and 2016, it was determined that indicators of impairment were present for certain shops as a result of continued underperformance. The Company performed an impairment analysis related to these shops and recorded impairment charges of $13.4 million, $10.6 million and $4.0 million for the fiscal years 2018, 2017 and 2016, respectively.

(k) Intangible Assets

The Company reviews indefinite-lived intangible assets, which includes goodwill and tradenames, annually at fiscal year-end for impairment or more frequently if events or circumstances indicate that the carrying value may not be recoverable. An impaired asset is written down to its estimated fair value based on the most recent information available. The Company assesses the fair values of its intangible assets, and its reporting unit for goodwill testing purposes, using an income-based approach. Under the income approach, fair value is based on the present value of estimated future cash flows. The income approach is dependent on a number of factors, including forecasted revenues and expenses, appropriate discount rates and other variables. The annual impairment review utilizes the estimated fair value of the intangible assets and the overall reporting unit and compares the estimated fair values to the carrying values as of the testing date. If the carrying value of these intangible assets or the reporting unit exceeds the fair values, the Company would then use the fair values to measure the amount of any required impairment charge. No impairment charge was recognized for intangible assets for any of the fiscal periods presented.

(l) Pre-opening Costs

Pre-opening costs consist of costs incurred prior to opening a new shop and are made up primarily of travel, employee payroll and training costs incurred prior to the shop opening, as well as occupancy costs incurred from when the Company takes site possession to shop opening. Shop pre-opening costs are expensed as incurred.

(m) Advertising Expenses

Advertising costs are expensed as incurred and are included in general and administrative expenses in the consolidated statements of operations. Advertising expenses were $4.3 million, $3.4 million and $3.0 million in fiscal years 2018, 2017 and 2016, respectively.

(n) Income Taxes

Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are attributed to differences between financial statement and income tax reporting. Deferred tax assets, net of any valuation allowances, represent the future tax return consequences of those differences and for operating loss and tax credit carryforwards, which will be deductible when the assets are recovered. Deferred tax assets are reduced by a valuation allowance if it is deemed more likely than not that some or all of the deferred tax assets will not be realized. In making this assessment of realizability of deferred tax assets, the Company considers all positive and negative evidence as to whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. The Company considers the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies in making this assessment. Deferred tax liabilities are recognized for temporary differences that will be taxable in future years’ tax returns.

The Company accounts for uncertain tax positions under current accounting guidance, which prescribes a minimum probability threshold that a tax position must meet before a financial statement benefit is recognized. The minimum threshold is defined as a tax position that is more likely than not to be sustained upon examination by tax authorities, based on the technical merits of the position. The tax benefit to be recognized is measured as the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement.

(o) Stock-Based Compensation

The Company has granted stock options under its 2001 Equity Incentive Plan (the “2001 Plan”), 2004 Equity Incentive Plan (the “2004 Plan”) and 2013 Long-Term Incentive Plan, as amended (the “2013 Plan” and together with the 2004 Plan and 2001 Plan, the “Plans”) and restricted stock units (“RSUs”) under its 2013 Plan. The Plans permit the granting of awards to employees and non-employee officers, consultants, agents, and independent contractors of the Company in the form of stock appreciation rights, stock awards and units, and stock options. The Plans give broad powers to the Company’s board of directors to administer and interpret the Plans, including the authority to select the individuals to be granted options and rights and to prescribe the particular form and conditions of each option to be granted. In September 2011, the 2001 Plan expired with options outstanding under the plan still available for exercise. On July 31, 2013, the Company’s board of directors approved the adoption of the 2013 Plan, which replaced the 2004 Plan in conjunction with the Company’s IPO. Upon approval of the 2013 Plan, the Company no longer issued awards under the 2004 Plan. The 2004 Plan expired in February 2014, but will continue to govern outstanding awards granted prior to its termination.

The Company accounts for its stock-based compensation in accordance with Accounting Standards Codification (“ASC”) 718, Stock Based Compensation. For employees, the Company records stock compensation expense on a straight-line basis over the vesting period based on the grant-date fair value of the awards, which is determined using the Black-Scholes option pricing valuation model for stock options and the quoted share price of Potbelly’s common stock on the date of grant for RSUs. For the Company’s non-employee directors, the Company records stock compensation expense on the grant date of the RSUs.

(p) Leases

The Company leases retail shops, warehouse and office space under operating leases. Most lease agreements contain tenant improvement allowances, rent holidays, lease premiums, rent escalation clauses, and/or contingent rent provisions. For purposes of recognizing incentives, premiums, and minimum rental expenses on a straight-line basis over the terms of the leases, the Company uses the date it takes possession of the leased space for construction purposes as the beginning of the term, which is generally two to three months prior to a shop’s opening date. For leases with renewal periods at the Company’s option, the Company determines the expected lease period based on whether the renewal of any options are reasonably assured at the inception of the lease. In addition to rental expense, certain leases require the Company to pay a portion of real estate taxes, utilities, building operating expenses, insurance and other charges in addition to rent.

For tenant improvement allowances, rent escalations, and rent holidays, the Company records a deferred rent liability in its consolidated balance sheets and amortizes the deferred rent over the terms of the leases as reductions to occupancy expense in the consolidated statements of operations.

(q) Revenue Recognition

Revenue from retail shops is presented net of discounts and recognized when food and beverage products are sold. Sales taxes collected from customers are excluded from revenues and the obligation is included in accrued liabilities until the taxes are remitted to the appropriate taxing authorities. The company adopted ASC 606 as January 1, 2018 using the modified retrospective method applied to contracts that were not completed as of the date of adoption.

Potbelly sells gift cards to customers, records the sale as a contract liability and recognizes the associated revenue as the gift card is redeemed. A portion of these gift cards are not redeemed by the customer, which is recognized by the Company as revenue as a percentage of customers gift card redemptions. The expected breakage amount recognized is determined by a historical data analysis on gift card redemption patterns. The Company recognized gift card breakage income of $312 thousand, $396 thousand and $254 thousand for the fiscal years ended 2018, 2017 and 2016, respectively, which is recorded within other operating expenses in the consolidated statements of operations.

The Company earns an initial franchise fee, a franchise development agreement fee and ongoing royalty fees under the Company’s franchise agreements. Prior to 2018, initial franchise fees were recognized as revenue when the shop opened. These franchise fees are considered highly dependent upon and interrelated with the franchise right granted in the franchise agreement. As such, these franchise fees are recognized over the contractual term of the franchise agreement. Under the new method, the Company recognized franchise fee revenue of 0.8 million in fiscal year 2018. Under the previous method, the Company recognized franchise fee revenue of $0.7 million and $0.4 million in fiscal year 2017 and 2016, respectively. The Company records a contract liability for the unearned portion of the upfront franchise payments. The Company has deferred revenue related to initial franchise fees of $1.2 million and $0.7 million included in accrued expenses as of December 30, 2018 and December 31, 2017, respectively. Franchise development agreement fees represent the exclusivity rights for a geographical area paid by a third party to develop Potbelly shops for a certain period of time. Franchise development agreement fee payments received by the Company are recorded as deferred revenue in the consolidated balance sheet and amortized over the life of the franchise development agreement. The Company had deferred revenue related to franchise development agreement fees of $0.7 million and $0.5 million recorded in accrued expenses as of December 30, 2018 and December 31, 2017, respectively. Royalty fees are based on a percentage of sales and are recorded as revenue as the fees are earned and become receivable from the franchisee. The Company recognized royalty fees revenue of $2.4 million, $2.5 million and $1.9 million for fiscal years 2018, 2017, and 2016, respectively.

(r) Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, “Revenue from Contracts with Customers.” The pronouncement was issued to clarify the principles for recognizing revenue and to develop a common revenue standard and disclosure requirements for U.S. GAAP and International Financial Reporting Standards (IFRS). In addition, the FASB issued ASU 2016-08, ASU 2016-10, ASU 2016-12, ASU 2016-20, ASU 2017-13 and ASU 2017-14 in March 2016, April 2016, May 2016, December 2016, September 2017 and November 2017, respectively, to help provide interpretive clarifications on the new guidance in Accounting Standards Codification (ASC) Topic 606. Potbelly adopted the standard effective January 1, 2018 using the modified retrospective method applied to contracts that were not completed as of the date of adoption. The adoption does not have a material impact on sandwich shop sales, but impacted the recognition of franchise revenue and gift card breakage. Potbelly licenses intellectual property and trademarks to franchisees through franchise arrangements. As part of these agreements, Potbelly receives an initial franchise fee payment which historically was recognized as revenue when the shop opened. Under the new guidance, these franchise fees are considered highly dependent upon and interrelated with the franchise right granted in the franchise agreement. As such, these franchise fees are recognized over the contractual term of the franchise agreement. Effective for the annual period beginning January 1, 2018, initial franchise fees are recognized as revenue over the contractual term. Potbelly sells gift cards to customers and records the sale as a liability. The liability is released once the card is redeemed. Historically, a portion of these gift card sales were not redeemed by the customer (“breakage”) and Potbelly would recognize breakage two years after the period of sale. Effective for the annual period beginning January 1, 2018, expected breakage is recognized as customers redeem the gift cards. Upon adoption of the standard, Potbelly’s accumulated deficit increased by $0.7 million (net of tax). The franchise revenue adjustment impacted accrued expenses, other long-term liabilities and deferred income taxes. The breakage adjustment impacted accrued expenses and deferred income taxes. Revenue recognized in the fiscal year 2018 was $0.1 million higher than it would have been under the previous methodology.

In February 2016, the FASB issued ASU No. 2016-02, “Leases,” which will replace the existing guidance in ASC 840, “Leases.” The pronouncement requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use asset and a corresponding lease liability. For finance leases, the lessee will recognize interest expense and amortization of the right-of-use asset and for operating leases, the lessee will recognize expense on a straight-line basis. The pronouncement is effective for fiscal years beginning after December 15, 2018, including annual and interim periods thereafter. We have elected the optional transition method to apply the standard as of the effective date and therefore, we will not apply the standard to the comparative periods presented in our financial statements. On the date of adoption, we will recognize a cumulative-effect adjustment in retained earnings due to impairment of certain right-of-use assets as of the effective date. We will elect the transition package of three practical expedients permitted within the standard, which eliminates the requirements to reassess prior conclusions about lease identification, lease classification, and initial direct costs. We will not elect the hindsight practical expedient, which permits the use of hindsight when determining lease term and impairment of right-of-use assets. Further, we will elect a short-term lease exception policy, permitting us to not apply the recognition requirements of this standard to short-term leases (i.e. leases with terms of 12 months or less) and an accounting policy to account for lease and non-lease components as a single component for certain classes of assets. We are still assessing the impact of the standard on our accounting policies, processes, disclosures, consolidated statements of operations, and internal control over financial reporting and have implemented necessary changes to our existing lease system to report in accordance with the new standard.

The adoption of ASU 2016-02 will have a significant impact on our consolidated balance sheets as we will record material assets and obligations primarily related to 437 restaurant operating leases and corporate office lease. We expect to record operating lease liabilities in a range of approximately $235 million to $255 million based on the present value of the remaining minimum rental payments using incremental borrowing rates as of the effective date. We expect to record corresponding right-of-use assets, based upon the operating lease liabilities adjusted for impairment of right-of-use assets recorded in retained earnings at December 31, 2018, prepaid and deferred rent, and unamortized initial direct costs. We expect no material impact on our consolidated statements of cash flows.

In March 2016, the FASB issued ASU No. 2016-09, “Compensation – Stock Compensation (Topic 718).” The pronouncement simplifies the accounting for the taxes related to stock-based compensation, including the accounting for income taxes, forfeitures and statutory tax withholding requirements, as well as classification within the statement of cash flows. The pronouncement is effective for annual periods beginning after December 15, 2016, including annual and interim periods. Potbelly adopted ASU 2016-09 in the first quarter of 2017. The primary impact of adoption was the recognition of excess tax benefits and deficiencies that arise upon vesting or exercise of share-based payments in the Income Statement as income tax expense instead of a component of equity recorded to paid-in capital. This aspect of the new guidance, which was required to be adopted prospectively, resulted in an additional income tax expense of $2.1 million for the fiscal year 2017. Potbelly has elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost to be recognized in each period. Excess income tax benefits and deficiencies from stock-based compensation arrangements are now classified as cash flow from operations, instead of as cash flow used in financing activities. The Company elected to apply this change in presentation prospectively and as such prior periods have not been adjusted. Additionally, in accordance with the new standard, the Company now excludes excess tax benefits and deficiencies from the assumed proceeds available to repurchase shares in the computation of the Company’s diluted earnings per share.

(s) Commitments and Contingencies

The Company is subject to legal proceedings including claims and liabilities, such as employment-related claims and slip and fall cases, which arise in the ordinary course of business and are generally covered by insurance. The Company accrues for such liabilities when it is probable that future costs will be incurred and such costs can be reasonably estimated. Such accruals are based on developments to date, the Company’s estimates of the outcomes of these matters and its experience in contesting, litigating and settling other similar matters. The Company believes resolution of these matters, individually and in the aggregate, will not have a material adverse effect on the Company’s financial position, liquidity or future operations.

Many of the food products the Company purchases are subject to changes in the price and availability of food commodities, including, among other things, beef, poultry, grains, dairy and produce. The Company works with its suppliers and uses a mix of forward pricing protocols for certain items including agreements with its supplier on fixed prices for deliveries at a time in the future and agreements on a fixed price with its supplier for the duration of those protocols. The Company also utilizes formula pricing protocols under which the prices the Company pays are based on a specified formula related to the prices of the goods, such as spot prices. The Company’s use of any forward pricing arrangements varies substantially from time to time and these arrangements tend to cover relatively short periods (i.e., typically twelve months or less). Such contracts are used in the normal purchases of the Company’s food products and not for speculative purposes, and as such are not required to be evaluated as derivative instruments.

Fair Value Measurement

12 Months Ended

Dec. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurement

(3) Fair Value Measurement

The carrying amounts of cash and cash equivalents, accounts receivable, accounts payable and all other current liabilities approximate fair values due to the short maturities of these balances.

The Company assesses potential impairments to its long-lived assets, which includes property and equipment, on a quarterly basis or whenever events or circumstances indicate that the carrying amount of an asset may not be recoverable. Shop-level assets are grouped at the individual shop-level for the purpose of the impairment assessment. Recoverability of an asset is measured by a comparison of the carrying amount of an asset to its estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of the asset group exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset exceeds the fair value of the asset. The fair value of the shop assets was determined using the discounted future cash flow method of anticipated cash flows through the shop’s lease-end date using fair value measurement inputs classified as Level 3. Level 3 inputs are derived from valuation techniques in which one or more significant inputs or significant value drivers are unobservable. After performing a periodic review of the Company’s shops during each quarter of 2018, 2017 and 2016, it was determined that indicators of impairment were present for certain shops as a result of continued underperformance. The Company performed an impairment analysis related to these shops and recorded impairment charges of $13.4 million, $10.6 million and $4.0 million for the fiscal years 2018, 2017 and 2016, respectively.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Earnings (Loss) Per Share

12 Months Ended

Dec. 30, 2018

Earnings Per Share [Abstract]

Earnings (Loss) Per Share

(4) Earnings (Loss) Per Share

Basic and diluted income per common share attributable to common stockholders are calculated using the weighted average number of common shares outstanding for the period. Diluted income per common share attributable to common stockholders is computed by dividing the income allocated to common stockholders by the weighted average number of fully diluted common shares outstanding. In periods of a net loss, no potential common shares are included in diluted shares outstanding as the effect is anti-dilutive. For the fiscal year 2018, the Company had a loss per share, therefore, shares were excluded for potential stock option exercises.

The following table summarizes the earnings (loss) per share calculation:

	Fiscal Year
	2018			2017			2016
Net income (loss) attributable to Potbelly Corporation	$	(8,878	)	$	(6,956	)	$	8,212
Weighted average common shares outstanding-basic		25,173,171			25,045,427			25,623,809
Plus: Effect of potential stock options exercise		—			—			549,578
Plus: Effect of potential warrant exercise		—			—			57,980
Weighted average common shares outstanding-diluted		25,173,171			25,045,427			26,231,367
Income (loss) per share available to common stockholders- basic	$	(0.35	)	$	(0.28	)	$	0.32
Income (loss) per share available to common stockholders- diluted	$	(0.35	)	$	(0.28	)	$	0.31
Potentially dilutive shares that are considered anti-dilutive:
Shares		2,499,139			3,375,591			1,164,047

Property and Equipment

12 Months Ended

Dec. 30, 2018

Property Plant And Equipment [Abstract]

Property and Equipment

(5) Property and Equipment

Property and equipment, net consisted of the following (in thousands):

	December 30,			December 31,
	2018			2017
Leasehold improvements	$	169,300		$	174,602
Machinery and equipment		48,606			49,427
Furniture and fixtures		33,177			33,893
Computer equipment and software		35,159			29,832
Construction in progress		1,938			3,831
		288,180			291,585
Less: Accumulated depreciation		(200,398	)		(187,726	)
	$	87,782		$	103,859

Accrued Expenses

12 Months Ended

Dec. 30, 2018

Accrued Liabilities Current [Abstract]

Accrued Expenses

(6) Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	December 30,		December 31,
	2018		2017
Accrued labor and related expenses	$	10,324	$	7,352
Deferred gift card revenue		1,821		2,305
Accrued occupancy expenses		2,309		2,387
Deferred rent—current		1,250		1,011
Accrued corporate and shop expenses		1,446		1,882
Accrued utilities		1,304		1,311
Accrued sales and use tax		3,001		2,760
Accrued construction		147		891
Accrued contract termination costs ^(a)		392		27
Accrued legal and professional fees		128		177
Accrued other		2,907		3,170
Total	$	25,029	$	23,273

(a)	The Company incurs expenses associated with exit activity for certain signed lease agreements, which are recognized in general and administrative expenses. Accrued contract termination costs consisted of the following (in thousands):

	December 30,			December 31,
	2018			2017
Accrued contract termination costs—beginning balance	$	27		$	28
Contract termination costs incurred		1,461			578
Contract termination costs settled and paid		(1,096	)		(579	)
Accrued contract termination costs—ending balance	$	392		$	27

Income Taxes

12 Months Ended

Dec. 30, 2018

Income Tax Disclosure [Abstract]

Income Taxes

(7) Income Taxes

Income (loss) before income taxes for the Company’s domestic and foreign operations was as follows (in thousands):

	Fiscal Year
	2018			2017			2016
Domestic operations	$	(11,381	)	$	(2,513	)	$	12,411
Foreign operations		637			466			468
Total	$	(10,744	)	$	(2,047	)	$	12,879

Income tax expense (benefit) consisted of the following (in thousands):

	Fiscal Year
	2018			2017			2016
Federal:
Current	$	(339	)	$	(3,728	)	$	4,652
Deferred		(1,644	)		8,792			(1,386	)
		(1,983	)		5,064			3,266
State and Local:
Current		73			150			1,426
Deferred		(305	)		(584	)		(273	)
		(232	)		(434	)		1,153
Foreign:
Current		20			13			24
		20			13			24
Income tax expense (benefit)	$	(2,195	)	$	4,643		$	4,443

Income tax expense (benefit) differed from the amounts computed by applying the U.S. federal income tax rates to income (loss) before income taxes as a result of the following (in thousands):

	Fiscal Year
	2018			2017			2016
U.S. federal statutory tax		21.0	%		35.0	%		35.0	%
Computed “expected” tax expense (benefit)	$	(2,256	)	$	(716	)	$	4,508
Increase (reduction) resulting from:
Minority interest		(87	)		(105	)		(89	)
Permanent differences		220			96			131
State and local income taxes, net of federal income tax effect		(436	)		5			673
FICA and other tax credits		(522	)		(502	)		(556	)
Equity compensation		1,089			2,112			—
Adjustments		(252	)		(93	)		(300	)
Rate change		49			3,846			76
	$	(2,195	)	$	4,643		$	4,443

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) was enacted into law making significant changes to the U.S. tax code, including: (1) reducing the U.S. federal corporate tax rate from 35 percent to 21 percent; (2) implementing bonus depreciation that will allow for full expensing of qualified property; (3) implementing limitations on the deductibility of certain executive compensation; and (4) changing rules related to uses and limitations of net operating loss carryforwards created in tax years beginning after December 31, 2017. At December 31, 2017, the Company had not completed the accounting for the tax effects of enactment of the Tax Act; however, the Company made a reasonable estimate which was recorded in the fourth quarter of 2017. During 2018, the Company made no changes to its initial estimates recorded at December 31, 2017 or the effective tax rate for 2018. As of December 30, 2018, the Company has completed its accounting related to the tax effects of enactment of the Tax Act.

Due to the adoption of ASU 2016-09 in 2017, all excess tax benefits and deficiencies are recognized as income tax expense in the Company’s Consolidated Statement of Operations.

The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities reflected in the consolidated balance sheets are presented below (in thousands):

	December 30,			December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	576		$	11
Accrued liabilities		1,449			842
Deferred revenue		543			120
Stock-based compensation		2,685			4,495
Property and equipment		5,037			3,258
Deferred rent		4,373			4,229
Tax credits and charitable contribution carryforwards		981			273
Other		—			127
Total deferred tax assets		15,644			13,355
Net deferred tax assets		15,644			13,355
Deferred tax liabilities:
Prepaids		(466	)		(452	)
Intangible assets		(1,075	)		(977	)
Smallwares		(566	)		(574	)
Other		(152	)		(150	)
Total deferred tax liabilities		(2,259	)		(2,153	)
Net deferred tax assets	$	13,385		$	11,202

As of December 30, 2018 and December 31, 2017, the Company has no valuation allowances recorded based on management’s assessment of the amount of its deferred tax assets that are more likely than not to be realized.

In assessing the realizability of deferred tax assets, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax planning strategies, and results of recent operations. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. As of December 30, 2018 and December 31, 2017, the Company has no valuation allowances recorded based on management’s assessment of the amount of its deferred tax assets that are more likely than not to be realized. The Company continues to monitor its operating performance and evaluate the likelihood of the future realization of these deferred tax assets. If actual operating results differ from our projections, or if future shop impairment charges are significant, a valuation allowance may be necessary.

In accordance with its accounting policy, the Company recognizes accrued interest and penalties related to unrecognized tax benefits as a component of income tax expense. As of December 30, 2018 and December 31, 2017, the Company had no interest or penalties accrued.

The tax years prior to 2014 are generally closed for examination by the United States Internal Revenue Service. However, certain of these tax years are open for examination as a result of net operating losses generated in these years and utilized in subsequent years. The Company’s last IRS examination was for the 2014 tax year; no IRS audits are currently ongoing. State statutes are generally open for audit for the 2015 to 2018 tax years. Additionally, certain tax years through 2018 are open for examination by certain state tax authorities.

Debt and Credit Facilities

12 Months Ended

Dec. 30, 2018

Debt Disclosure [Abstract]

Debt and Credit Facilities

(8) Debt and Credit Facilities

Credit facility

JPMorgan Chase Bank, N.A.

On December 9, 2015, the Company entered into an amended and restated five-year revolving credit facility agreement that expires in November 2020. The credit agreement provides, among other things, for a revolving credit facility in a maximum principal amount of $50 million, with possible future increases to $75 million under an expansion feature. Borrowings under the credit facility generally bear interest at the Company’s option at either (i) a eurocurrency rate determined by reference to the applicable LIBOR rate plus a margin ranging from 1.00% to 1.75% or (ii) a prime rate as announced by JP Morgan Chase plus a margin ranging from 0.00% to 0.50%. The applicable margin is determined based upon the Company’s consolidated total leverage ratio. On the last day of each calendar quarter, the Company is required to pay a commitment fee ranging from 0.125% to 0.20% per annum in respect of any unused commitments under the credit facility, with the specific rate determined based upon the Company’s consolidated total leverage ratio. So long as certain total leverage ratios are met, there is no limit on the “restricted payments” (primarily distributions and equity repurchases) that the Company may make. As of December 30, 2018 the Company had no amounts outstanding under the credit facility.

Capital Stock and Warrants

12 Months Ended

Dec. 30, 2018

Equity [Abstract]

Capital Stock and Warrants

(9) Capital Stock and Warrants

As of December 30, 2018 and December 31, 2017, the Company had authorized an aggregate of 210,000,000 shares of capital stock, of which 200,000,000 shares were designated as common stock and 10,000,000 shares were designated as preferred stock. As of December 30, 2018, the Company had issued and outstanding 32,943,740 and 24,142,586 shares of common stock, respectively. As of December 31, 2017, the Company had issued and outstanding 31,831,196 and 24,999,688 shares of common stock, respectively.

Common Stock

As of December 30, 2018, each share of common stock has the same relative rights and was identical in all respects to each other share of common stock. Each holder of shares of common stock is entitled to one vote for each share held by such holder at all meetings of stockholders.

On May 8, 2018, the Company announced that its Board of Directors authorized a stock repurchase program for up to $65.0 million of its outstanding common stock, replacing the Company’s previous $30.0 million share repurchase program. The current program permits the Company, from time to time, to purchase shares in the open market (including in pre-arranged stock trading plans in accordance with the guidelines specified in Rule 10b5-1 under the Securities Exchange Act of 1934, as amended) or in privately negotiated transactions. The number of common shares actually repurchased, and the timing and price of repurchases, will depend upon market conditions, Securities and Exchange Commission requirements and other factors. Purchases may be started or stopped at any time without prior notice depending on market conditions and other factors. During the fiscal year 2018, the Company repurchased 1,948,245 shares of its common stock for approximately $22.9 million under the new stock repurchase program and had repurchased 5,000 shares of its common stock for approximately $0.1 million under the previous share repurchase program, including cost and commission, in open market transactions. As of December 30, 2018, the remaining dollar value of authorization under the share repurchase program was $42.1 million, which does not include commission. Repurchased shares are included as treasury stock in the condensed consolidated balance sheets and the condensed consolidated statements of equity.

On June 14, 2018, the Company registered 1,000,000 additional shares of its common stock, par value $0.01, reserved for issuance under the Amended and Restated 2013 Long-Term Incentive Plan. As a result, the total number of shares registered under the 2013 Long-Term Incentive Plan is 3,500,000.

Warrants

The Company had zero warrants outstanding as of both December 30, 2018 and December 31, 2017. Outstanding warrants were exercised in June 2017 with proceeds of $2.0 million received by the Company.

Operating Leases

12 Months Ended

Dec. 30, 2018

Leases [Abstract]

Operating Leases

(10) Operating Leases

The Company leases office space for its corporate office and commercial spaces for its shops under various long-term operating lease agreements. The leases for the Company’s shop locations generally have initial terms of 10 years and typically provide for two renewal options in five-year increments as well as for rent escalations. These leases expire or become subject to renewal clauses at various dates from 2019 to 2028. Some of the leases provide for base rent, plus additional rent based on gross sales, as defined in each lease agreement. The Company is also generally obligated to pay certain real estate taxes, utilities, building operating expenses, insurance, and various other expenses related to properties.

Rental expense under operating lease agreements were as follows (in thousands):

	Fiscal Year
	2018		2017			2016
Minimum rentals	$	46,334	$	45,334		$	40,252
Contingent rentals		1,295		1,408			1,755
Less: sublease rentals		—		(33	)		(94	)
Total	$	47,629	$	46,709		$	41,913

A schedule by year of future minimum rental payments required under operating leases, excluding contingent rent, that have initial or remaining non-cancelable lease terms in excess of one year, as of December 30, 2018, is as follows (in thousands):

Years Ending	Minimum
2019		47,918
2020		45,828
2021		41,497
2022		36,120
2023		31,060
Thereafter		138,928
Total minimum payments required*	$	341,351

*	Minimum payments have not been reduced by minimum sublease rentals of $1.6 million due in the future.

Certain leases have outstanding letters of credit in lieu of rent deposits expiring at various dates through September 2019. The letters of credit were $0.2 million, $0.2 million and $0.7 million in aggregate for the fiscal years ended December 30, 2018, December 31, 2017 and December 25, 2016, respectively. Under the credit facility, outstanding letters of credit are subject to an annual fee of 1.5% and reduce the available borrowing to the Company.

Employee Benefit Plan

12 Months Ended

Dec. 30, 2018

Postemployment Benefits [Abstract]

Employee Benefit Plan

(11) Employee Benefit Plan

The Company sponsors a 401(k) profit sharing plan for all employees who are eligible based upon age and length of service. The Company made matching contributions of $0.4 million for fiscal years 2018, 2017 and 2016.

Stock-Based Compensation

12 Months Ended

Dec. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

(12) Stock-Based Compensation

Stock-Based Compensation Granted Under the 2013 Long-Term Incentive Plan

Stock options and restricted stock units are awarded under the 2013 Long-Term Incentive Plan to eligible employees and certain non-employee members of the Board of Directors. The 2013 Plan gives broad powers to the Company’s Board of Directors to administer and interpret the 2013 Plan, including the authority to select the individuals to be granted equity awards and rights and to prescribe the particular form and conditions of each equity award to be granted.

On July 31, 2013, the Company’s Board of Directors approved the adoption of the 2013 Plan, which replaced the 2004 Equity Incentive Plan (the “2004 Plan” and together with the 2013 Plan, the “Plans”) in conjunction with the Company’s IPO. Upon approval of the 2013 Plan, the Company no longer issued awards under the 2004 Plan. The 2004 Plan expired in February 2014, but will continue to govern outstanding awards granted prior to its termination. As of December 30, 2018, there have been 2,514,194 options, 28,240 shares of common stock and 460,855 shares of restricted stock units granted under the 2013 Plan. As of May 2018, restricted stock units granted under the 2013 Plan count against shares reserved for future issuances at a ratio of 2:1. As of December 30, 2018, there are 1,699,387 shares reserved for future issuance.

Stock Options

Under the Plans, the number of shares and exercise price of each option are determined by the committee designated by the Company’s Board of Directors. The options granted are generally exercisable within a 10-year period from the date of grant. The company awards options to certain employees including the senior leadership team. Options outstanding expire on various dates through the year 2028. The range of exercise prices for options outstanding as of December 30, 2018 is $7.00 to $20.53 per option, and the options generally vest in one-fourth and one-fifth increments over four and five-year periods, respectively.

Activity under the Plans and the Agreement is as follows:

Options	Shares (Thousands)			Weighted Average Exercise Price		Aggregate Intrinsic Value (Thousands)		Weighted Average Remaining Term (Years)
Outstanding—December 27, 2015		4,368		$	10.53	$	9,742		5.10
Granted		369			13.65
Exercised		(536	)		10.77
Canceled		(188	)		14.40
Outstanding—December 25, 2016		4,013		$	10.61	$	13,455		4.78
Granted		464			12.09
Exercised		(653	)		9.94
Canceled		(515	)		12.18
Outstanding—December 31, 2017		3,309		$	10.71	$	7,699		4.90
Granted		203			11.27
Exercised		(993	)		8.30
Canceled		(369	)		13.63
Outstanding—December 30, 2018		2,150		$	11.49	$	378		5.13
Exercisable—December 30, 2018		1,611		$	11.14	$	378		4.52

The following table reflects the average assumptions utilized in the Black-Scholes option-pricing model to value the options granted for each year:

	2018			2017			2016
Risk-free interest rate		3.0	%		2.0	%		1.7	%
Expected life (years)		6.25			6.25			7.00
Expected dividend yield		—			—			—
Volatility		35.0	%		36.0	%		49.4	%
Weighted average grant date fair value	$	4.52		$	4.76		$	7.05

The risk-free rate is based on U.S. Treasury rates in effect at the time of the grant with a similar duration of the expected life of the options. The expected life of options granted is derived from the average of the vesting period and the term of the option. The Company has not paid dividends to date (with exception to the one-time dividend paid to stockholders prior to the initial public offering) and does not plan to pay dividends in the near future.

RSUs

The Company awards restricted stock units (“RSUs”) to certain non-employee members of its Board of Directors and the senior leadership team. In May 2018, the Company issued 74,760 shares of RSUs with a grant date fair value of $13.25 upon issuance. In June 2018, the Company issued 19,157 RSUs with a grant date fair value of $13.05 upon issuance. In December 2018, the Company issued 37,353 RSUs with a grant date fair value of $9.37 upon issuance. The Board of Director grants have a vesting schedule of 50% on the first anniversary of the grant date and 50% on the second anniversary of the grant date. The senior leadership team grants vest in one-third increments over a three-year period.

In May 2017, the Company issued 153,369 shares of RSUs with a grant date fair value of $11.05 upon issuance. In August 2017, the Company issued 2,608 shares of RSUs with a grant date fair value of $11.15 upon issuance. In November 2017, the Company issued 6,848 and 78,125 shares of RSUs with grant date fair values of $11.50 and $12.80 upon issuance, respectively. In May 2016, the Company issued 52,558 shares of RSUs with a grant date fair value of $13.27 upon issuance.

Stock-Based Compensation Expense

Stock-based compensation is measured at the grant date, based on the calculated fair value of the award and is recognized as expense over the requisite employee service period, which is generally the vesting period of the grant, with a corresponding increase to additional paid-in-capital. For the fiscal year 2018, the Company recognized stock compensation expense of $2.9 million. For the fiscal years 2017 and 2016, the company recognized stock compensation expense of $4.7 million and $3.1 million, respectively. As of December 30, 2018, unrecognized stock-based compensation expense was $3.0 million, which will be recognized through fiscal year 2022. The Company records stock-based compensation expense within general and administrative expenses in the consolidated statements of operations.

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 30, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (Unaudited)

(13) Quarterly Financial Data (Unaudited)

The unaudited quarterly information includes all normal recurring adjustments that the Company considers necessary for the fair presentation of the information shown below. The Company’s quarterly results have been and will continue to be affected by the timing of new shop openings and their associated pre-opening costs. As a result of these and other factors, the financial results for any quarter may not be indicative of the results for any future period.

The following table presents selected unaudited quarterly financial data for periods indicated (in thousands, except per share data):

	Fiscal Year 2018 (1)
	April 1			July 1			September 30			December 30
Total revenues	$	102,917		$	110,347		$	106,996		$	102,378
Income (loss) from operations		(2,630	)		95			(2,697	)		(5,370	)
Net income attributable to Potbelly Corporation		(2,194	)		(360	)		(1,961	)		(4,363	)
Income per share available to common stockholders-basic		(0.09	)		(0.01	)		(0.08	)		(0.17	)
Income per share available to common stockholders-diluted		(0.09	)		(0.01	)		(0.08	)		(0.17	)

	Fiscal Year 2017 (1)
	March 26		June 25			September 24			December 31
Total revenues	$	101,699	$	108,136		$	106,127		$	112,149
Income from operations		1,263		164			(574	)		(2,776	)
Net income (loss) attributable to Potbelly Corporation		683		(138	)		(240	)		(7,261	)
Income (loss) per share available to common stockholders-basic		0.03		(0.01	)		(0.01	)		(0.29	)
Income (loss) per share available to common stockholders-diluted		0.03		(0.01	)		(0.01	)		(0.29	)

(1)	Fiscal year 2018 was a 52-week year. Each quarter of the fiscal year consisted of 13 weeks. Fiscal year 2017 was a 53-week year. The first three fiscal quarters consisted of 13 weeks and the fourth fiscal quarter consisted of 14 weeks.

Commitments and Contingencies

12 Months Ended

Dec. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

(14) Commitments and Contingencies

The Company is subject to legal proceedings, claims and liabilities, such as employment-related claims and slip and fall cases, which arise in the ordinary course of business and are generally covered by insurance. In the opinion of management, the amount of ultimate liability with respect to those actions should not have a material adverse impact on the Company’s financial position or results of operations and cash flows.

In October 2017, plaintiffs filed a purported collective and class action lawsuit (the “Complaint”) in the United States District Court for the Southern District of New York against the Company alleging violations of the Fair Labor Standards Act (FLSA) and New York Labor Law (NYLL). The plaintiffs allege that the Company violated the FLSA and NYLL by not paying overtime compensation to our assistant managers and violated NYLL by not paying spread-of-hours pay. The Complaint was brought as a nationwide “collective action” under the FLSA and as a “class action” under NYLL. Since the filing of the Complaint, the plaintiffs have stated that they do not intend to pursue the New York state class action. They have indicated, however, an intent to pursue an Illinois state law class action, but have not yet filed an amended complaint. Potbelly believes the assistant managers were properly classified under state and federal law. The Company intends to vigorously defend this action. This case is at an early stage, and Potbelly is therefore unable to make a reasonable estimate of the probable loss or range of losses, if any, that might arise from this matter.

Revenue

12 Months Ended

Dec. 30, 2018

Revenue From Contract With Customer [Abstract]

Revenue

(15) Revenue

Potbelly primarily earns revenue at a point in time through sales at our sandwich shop locations and records such revenue net of sales-related taxes collected from customers. The payment on these sales is due at the time of the customer’s purchase. The Company also receives royalties from franchisees on their respective sales, which are recognized at the point in time the sale is made and invoiced weekly. Potbelly also records revenue from sales over time related to upfront franchise fees, gift card redemptions and breakage. For the fiscal year ended December 30, 2018, revenue recognized from all revenue sources on point in time sales was $421.8 million, and revenue recognized from sales over time was $0.8 million.

Franchise Revenue

Potbelly licenses intellectual property and trademarks to franchisees through franchise agreements. As part of these franchise agreements, Potbelly receives an upfront payment from the franchisee, which the Company recognizes over the term of the franchise agreement. The Company records a contract liability for the unearned portion of the upfront franchise payments.

Gift Card Redemptions / Breakage Revenue

Contract Liabilities

As described above, the Company records current and noncurrent contract liabilities for upfront franchise fees as well as gift cards. There are no other contract liabilities or contract assets recorded by the Company. The opening and closing balances of the Company’s current and noncurrent contract liabilities from contracts with customers were as follows:

	Current Contract Liability			Noncurrent Contract Liability
	(Thousands)			(Thousands)
Beginning balance as of January 1, 2018	$	(2,325	)	$	(2,144	)
Ending balance as of December 30, 2018		(2,184	)		(1,631	)
Decrease in contract liability	$	(141	)	$	(513	)

The aggregate value of remaining performance obligations on outstanding contracts was $3.8 million as of December 30, 2018. The decrease in the liability during the 52 weeks ended December 30, 2018 was a result of gift card redemptions offset by purchases of new gift cards and recognition of franchise fees. The Company expects to recognize revenue related to contract liabilities as follows (in thousands), which may vary based upon franchise activity as well as gift card redemption patterns:

Years Ending	Amount
2019	$	2,184
2020	$	199
2021	$	195
2022	$	189
2023	$	501
Thereafter	$	547
Total revenue recognized	$	3,815

For the 52 weeks ended December 30, 2018, the amount of revenue recognized related to the January 1, 2018 liability ending balance was $2.1 million. This revenue related to the recognition of gift card redemptions and upfront franchise fees. For the year ended December 30, 2018, the Company did not recognize any revenue from obligations satisfied (or partially satisfied) in prior periods.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 30, 2018

Accounting Policies [Abstract]

Principles of Consolidation

(a) Principles of Consolidation

Reporting Period

(b) Reporting Period

Segment Reporting

Use of Estimates

(d) Use of Estimates

Fair Value Measurements

(e) Fair Value Measurements

•

Level 1 — Quoted prices in active markets for identical assets or liabilities.

•

Financial Instruments

(f) Financial Instruments

Cash and Cash Equivalents

(g) Cash and Cash Equivalents

Accounts Receivable, net

(h) Accounts Receivable, net

Inventories

(i) Inventories

Property and Equipment

(j) Property and Equipment

Intangible Assets

(k) Intangible Assets

Pre-opening Costs

(l) Pre-opening Costs

Advertising Expenses

(m) Advertising Expenses

Income Taxes

(n) Income Taxes

Stock-Based Compensation

(o) Stock-Based Compensation

Leases

(p) Leases

Revenue Recognition

(q) Revenue Recognition

Recent Accounting Pronouncements

(r) Recent Accounting Pronouncements

Commitments and Contingencies

(s) Commitments and Contingencies

Earnings (Loss) Per Share (Tables)

12 Months Ended

Dec. 30, 2018

Earnings Per Share [Abstract]

Summary of Earnings (Loss) Per Share Calculation

The following table summarizes the earnings (loss) per share calculation:

	Fiscal Year
	2018			2017			2016
Net income (loss) attributable to Potbelly Corporation	$	(8,878	)	$	(6,956	)	$	8,212
Weighted average common shares outstanding-basic		25,173,171			25,045,427			25,623,809
Plus: Effect of potential stock options exercise		—			—			549,578
Plus: Effect of potential warrant exercise		—			—			57,980
Weighted average common shares outstanding-diluted		25,173,171			25,045,427			26,231,367
Income (loss) per share available to common stockholders- basic	$	(0.35	)	$	(0.28	)	$	0.32
Income (loss) per share available to common stockholders- diluted	$	(0.35	)	$	(0.28	)	$	0.31
Potentially dilutive shares that are considered anti-dilutive:
Shares		2,499,139			3,375,591			1,164,047

Property and Equipment (Tables)

12 Months Ended

Dec. 30, 2018

Property Plant And Equipment [Abstract]

Components of Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

	December 30,			December 31,
	2018			2017
Leasehold improvements	$	169,300		$	174,602
Machinery and equipment		48,606			49,427
Furniture and fixtures		33,177			33,893
Computer equipment and software		35,159			29,832
Construction in progress		1,938			3,831
		288,180			291,585
Less: Accumulated depreciation		(200,398	)		(187,726	)
	$	87,782		$	103,859

Accrued Expenses (Tables)

12 Months Ended

Dec. 30, 2018

Accrued Liabilities Current [Abstract]

Summary of Accrued Expenses

Accrued expenses consisted of the following (in thousands):

	December 30,		December 31,
	2018		2017
Accrued labor and related expenses	$	10,324	$	7,352
Deferred gift card revenue		1,821		2,305
Accrued occupancy expenses		2,309		2,387
Deferred rent—current		1,250		1,011
Accrued corporate and shop expenses		1,446		1,882
Accrued utilities		1,304		1,311
Accrued sales and use tax		3,001		2,760
Accrued construction		147		891
Accrued contract termination costs ^(a)		392		27
Accrued legal and professional fees		128		177
Accrued other		2,907		3,170
Total	$	25,029	$	23,273

(a)	The Company incurs expenses associated with exit activity for certain signed lease agreements, which are recognized in general and administrative expenses. Accrued contract termination costs consisted of the following (in thousands):

	December 30,			December 31,
	2018			2017
Accrued contract termination costs—beginning balance	$	27		$	28
Contract termination costs incurred		1,461			578
Contract termination costs settled and paid		(1,096	)		(579	)
Accrued contract termination costs—ending balance	$	392		$	27

Summary of Accrued Contract Termination Costs

Accrued contract termination costs consisted of the following (in thousands):

	December 30,			December 31,
	2018			2017
Accrued contract termination costs—beginning balance	$	27		$	28
Contract termination costs incurred		1,461			578
Contract termination costs settled and paid		(1,096	)		(579	)
Accrued contract termination costs—ending balance	$	392		$	27

Income Taxes (Tables)

12 Months Ended

Dec. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Income (Loss) Before Income Taxes

Income (loss) before income taxes for the Company’s domestic and foreign operations was as follows (in thousands):

	Fiscal Year
	2018			2017			2016
Domestic operations	$	(11,381	)	$	(2,513	)	$	12,411
Foreign operations		637			466			468
Total	$	(10,744	)	$	(2,047	)	$	12,879

Components of Income Tax Expense (Benefit)

Income tax expense (benefit) consisted of the following (in thousands):

	Fiscal Year
	2018			2017			2016
Federal:
Current	$	(339	)	$	(3,728	)	$	4,652
Deferred		(1,644	)		8,792			(1,386	)
		(1,983	)		5,064			3,266
State and Local:
Current		73			150			1,426
Deferred		(305	)		(584	)		(273	)
		(232	)		(434	)		1,153
Foreign:
Current		20			13			24
		20			13			24
Income tax expense (benefit)	$	(2,195	)	$	4,643		$	4,443

Reconciliation of Differences Between Federal Statutory and Effective Income (Loss) Tax Rate

Income tax expense (benefit) differed from the amounts computed by applying the U.S. federal income tax rates to income (loss) before income taxes as a result of the following (in thousands):

	Fiscal Year
	2018			2017			2016
U.S. federal statutory tax		21.0	%		35.0	%		35.0	%
Computed “expected” tax expense (benefit)	$	(2,256	)	$	(716	)	$	4,508
Increase (reduction) resulting from:
Minority interest		(87	)		(105	)		(89	)
Permanent differences		220			96			131
State and local income taxes, net of federal income tax effect		(436	)		5			673
FICA and other tax credits		(522	)		(502	)		(556	)
Equity compensation		1,089			2,112			—
Adjustments		(252	)		(93	)		(300	)
Rate change		49			3,846			76
	$	(2,195	)	$	4,643		$	4,443

Schedule of Deferred Tax Assets and Liabilities

	December 30,			December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	576		$	11
Accrued liabilities		1,449			842
Deferred revenue		543			120
Stock-based compensation		2,685			4,495
Property and equipment		5,037			3,258
Deferred rent		4,373			4,229
Tax credits and charitable contribution carryforwards		981			273
Other		—			127
Total deferred tax assets		15,644			13,355
Net deferred tax assets		15,644			13,355
Deferred tax liabilities:
Prepaids		(466	)		(452	)
Intangible assets		(1,075	)		(977	)
Smallwares		(566	)		(574	)
Other		(152	)		(150	)
Total deferred tax liabilities		(2,259	)		(2,153	)
Net deferred tax assets	$	13,385		$	11,202

Operating Leases (Tables)

12 Months Ended

Dec. 30, 2018

Leases [Abstract]

Schedule Of Rental Expenses Under Operating Leases

Rental expense under operating lease agreements were as follows (in thousands):

	Fiscal Year
	2018		2017			2016
Minimum rentals	$	46,334	$	45,334		$	40,252
Contingent rentals		1,295		1,408			1,755
Less: sublease rentals		—		(33	)		(94	)
Total	$	47,629	$	46,709		$	41,913

Schedule of Future Minimum Rental Payments Under Operating Leases

Years Ending	Minimum
2019		47,918
2020		45,828
2021		41,497
2022		36,120
2023		31,060
Thereafter		138,928
Total minimum payments required*	$	341,351

*	Minimum payments have not been reduced by minimum sublease rentals of $1.6 million due in the future.

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Options Activity Under Plans and Agreement

Activity under the Plans and the Agreement is as follows:

Options	Shares (Thousands)			Weighted Average Exercise Price		Aggregate Intrinsic Value (Thousands)		Weighted Average Remaining Term (Years)
Outstanding—December 27, 2015		4,368		$	10.53	$	9,742		5.10
Granted		369			13.65
Exercised		(536	)		10.77
Canceled		(188	)		14.40
Outstanding—December 25, 2016		4,013		$	10.61	$	13,455		4.78
Granted		464			12.09
Exercised		(653	)		9.94
Canceled		(515	)		12.18
Outstanding—December 31, 2017		3,309		$	10.71	$	7,699		4.90
Granted		203			11.27
Exercised		(993	)		8.30
Canceled		(369	)		13.63
Outstanding—December 30, 2018		2,150		$	11.49	$	378		5.13
Exercisable—December 30, 2018		1,611		$	11.14	$	378		4.52

Schedule of Average Assumptions to Value Options

The following table reflects the average assumptions utilized in the Black-Scholes option-pricing model to value the options granted for each year:

	2018			2017			2016
Risk-free interest rate		3.0	%		2.0	%		1.7	%
Expected life (years)		6.25			6.25			7.00
Expected dividend yield		—			—			—
Volatility		35.0	%		36.0	%		49.4	%
Weighted average grant date fair value	$	4.52		$	4.76		$	7.05

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 30, 2018

Quarterly Financial Information Disclosure [Abstract]

Summary of Unaudited Quarterly Financial Data

The following table presents selected unaudited quarterly financial data for periods indicated (in thousands, except per share data):

	Fiscal Year 2018 (1)
	April 1			July 1			September 30			December 30
Total revenues	$	102,917		$	110,347		$	106,996		$	102,378
Income (loss) from operations		(2,630	)		95			(2,697	)		(5,370	)
Net income attributable to Potbelly Corporation		(2,194	)		(360	)		(1,961	)		(4,363	)
Income per share available to common stockholders-basic		(0.09	)		(0.01	)		(0.08	)		(0.17	)
Income per share available to common stockholders-diluted		(0.09	)		(0.01	)		(0.08	)		(0.17	)

	Fiscal Year 2017 (1)
	March 26		June 25			September 24			December 31
Total revenues	$	101,699	$	108,136		$	106,127		$	112,149
Income from operations		1,263		164			(574	)		(2,776	)
Net income (loss) attributable to Potbelly Corporation		683		(138	)		(240	)		(7,261	)
Income (loss) per share available to common stockholders-basic		0.03		(0.01	)		(0.01	)		(0.29	)
Income (loss) per share available to common stockholders-diluted		0.03		(0.01	)		(0.01	)		(0.29	)

(1)	Fiscal year 2018 was a 52-week year. Each quarter of the fiscal year consisted of 13 weeks. Fiscal year 2017 was a 53-week year. The first three fiscal quarters consisted of 13 weeks and the fourth fiscal quarter consisted of 14 weeks.

Revenue (Tables)

12 Months Ended

Dec. 30, 2018

Revenue From Contract With Customer [Abstract]

Summary of Current and Noncurrent Contract Liabilities from Contracts with Customers

The opening and closing balances of the Company’s current and noncurrent contract liabilities from contracts with customers were as follows:

	Current Contract Liability			Noncurrent Contract Liability
	(Thousands)			(Thousands)
Beginning balance as of January 1, 2018	$	(2,325	)	$	(2,144	)
Ending balance as of December 30, 2018		(2,184	)		(1,631	)
Decrease in contract liability	$	(141	)	$	(513	)

Summary of Expected Revenue Recognition Related to Contract Liabilities

The Company expects to recognize revenue related to contract liabilities as follows (in thousands), which may vary based upon franchise activity as well as gift card redemption patterns:

Years Ending	Amount
2019	$	2,184
2020	$	199
2021	$	195
2022	$	189
2023	$	501
Thereafter	$	547
Total revenue recognized	$	3,815

Organization and Other Matters - Additional Information (Detail)	Dec. 30, 2018 Shop
Minimum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shops Potbelly Corporation owns or operates	400
Middle East, Canada and India [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Number of shops franchisees operate	50

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended								12 Months Ended
	Dec. 30, 2018 USD ($) JointVenture Restaurant	Sep. 30, 2018 USD ($)	Jul. 01, 2018 USD ($)	Apr. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 24, 2017 USD ($)	Jun. 25, 2017 USD ($)	Mar. 26, 2017 USD ($)	Dec. 30, 2018 USD ($) Subsidiary JointVenture Segment Restaurant	Dec. 31, 2017 USD ($)	Dec. 25, 2016 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of wholly owned subsidiaries \| Subsidiary									8
Number of joint ventures \| JointVenture	6								6
Number of operating segments \| Segment									1
Number of reportable segments \| Segment									1
Credit card receivables	$ 2,000,000				$ 1,900,000				$ 2,000,000	$ 1,900,000
Impairment charges									13,400,000	10,600,000	$ 4,000,000
Recognized impairment for intangible assets									0	0	0
Advertising expenses									4,300,000	3,400,000	3,000,000
Gift card breakage income recognized									312,000	396,000	254,000
Revenue	102,378,000	$ 106,996,000	$ 110,347,000	$ 102,917,000	112,149,000	$ 106,127,000	$ 108,136,000	$ 101,699,000	$ 422,638,000	428,111,000	407,131,000
Term of breakage recognized after sale									2 years
Increase in accumulated deficit	(229,558,000)				(219,990,000)				$ (229,558,000)	(219,990,000)
Excess tax deficiency (benefit) from stock-based compensation									1,089,000	2,112,000	(31,000)
Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase in accumulated deficit	$ 700,000								700,000
Increase in revenue recognized									$ 100,000
Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of restaurants \| Restaurant	437								437
Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Excess tax deficiency (benefit) from stock-based compensation										2,100,000
Franchise Fee [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenue									$ 800,000	700,000	400,000
Royalty Fees [Member]
Summary Of Significant Accounting Policies [Line Items]
Revenue									2,400,000	2,500,000	$ 1,900,000
Initial Franchise Fees [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue	$ 1,200,000				700,000				1,200,000	700,000
Franchise Development Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred revenue	700,000				$ 500,000				$ 700,000	$ 500,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest rate									51.00%
Estimated period of time between Company's possession of leased space and shop opening date									2 months
Minimum [Member] \| Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease liability	235,000,000								$ 235,000,000
Minimum [Member] \| Computer Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									3 years
Minimum [Member] \| Computer Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									3 years
Minimum [Member] \| Machinery and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									3 years
Minimum [Member] \| Leasehold Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									10 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest rate									80.00%
Estimated period of time between Company's possession of leased space and shop opening date									3 months
Maximum [Member] \| Accounting Standards Update 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating lease liability	$ 255,000,000								$ 255,000,000
Maximum [Member] \| Computer Software [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									5 years
Maximum [Member] \| Furniture and Fixtures [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									5 years
Maximum [Member] \| Computer Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									5 years
Maximum [Member] \| Machinery and Equipment [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									5 years
Maximum [Member] \| Leasehold Improvements [Member]
Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful life									15 years

Fair Value Measurement - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Fair Value Disclosures [Abstract]
Impairment charges	$ 13.4	$ 10.6	$ 4.0

Earnings (Loss) Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Earnings (Loss) Per Share [Line Items]
Potential common shares included in diluted shares outstanding	2,499,139	3,375,591	1,164,047
Common Share Options [Member]
Earnings (Loss) Per Share [Line Items]
Potential common shares included in diluted shares outstanding	0

Earnings (Loss) Per Share - Summary of Earnings (Loss) Per Share Calculation (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Earnings Per Share [Abstract]
Net income (loss) attributable to Potbelly Corporation	$ (4,363)	$ (1,961)	$ (360)	$ (2,194)	$ (7,261)	$ (240)	$ (138)	$ 683	$ (8,878)	$ (6,956)	$ 8,212
Weighted average common shares outstanding-basic									25,173,171	25,045,427	25,623,809
Plus: Effect of potential stock options exercise											549,578
Plus: Effect of potential warrant exercise											57,980
Weighted average common shares outstanding-diluted									25,173,171	25,045,427	26,231,367
Income (loss) per share available to common stockholders-basic	$ (0.17)	$ (0.08)	$ (0.01)	$ (0.09)	$ (0.29)	$ (0.01)	$ (0.01)	$ 0.03	$ (0.35)	$ (0.28)	$ 0.32
Income (loss) per share available to common stockholders-diluted	$ (0.17)	$ (0.08)	$ (0.01)	$ (0.09)	$ (0.29)	$ (0.01)	$ (0.01)	$ 0.03	$ (0.35)	$ (0.28)	$ 0.31
Potentially dilutive shares that are considered anti-dilutive									2,499,139	3,375,591	1,164,047

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109260490&loc=d3e1337-109256

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Leasehold improvements	$ 169,300	$ 174,602
Machinery and equipment	48,606	49,427
Furniture and fixtures	33,177	33,893
Computer equipment and software	35,159	29,832
Construction in progress	1,938	3,831
Property and equipment, gross	288,180	291,585
Less: Accumulated depreciation	(200,398)	(187,726)
Property and equipment, net	$ 87,782	$ 103,859

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Accrued Liabilities And Other Liabilities [Abstract]
Accrued labor and related expenses	$ 10,324	$ 7,352
Deferred gift card revenue	1,821	2,305
Accrued occupancy expenses	2,309	2,387
Deferred rent—current	1,250	1,011
Accrued corporate and shop expenses	1,446	1,882
Accrued utilities	1,304	1,311
Accrued sales and use tax	3,001	2,760
Accrued construction	147	891
Accrued contract termination costs	392	27	$ 28
Accrued legal and professional fees	128	177
Accrued other	2,907	3,170
Total	$ 25,029	$ 23,273

Accrued Expenses - Summary of Accrued Contract Termination Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017
Accrued Liabilities And Other Liabilities [Abstract]
Accrued contract termination costs—beginning balance	$ 27	$ 28
Contract termination costs incurred	1,461	578
Contract termination costs settled and paid	(1,096)	(579)
Accrued contract termination costs—ending balance	$ 392	$ 27

Income Taxes - Schedule of Income (Loss) Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Income Tax Disclosure [Abstract]
Domestic operations	$ (11,381)	$ (2,513)	$ 12,411
Foreign operations	637	466	468
Income (loss) before income taxes	$ (10,744)	$ (2,047)	$ 12,879

Income Taxes - Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Income Tax Disclosure [Abstract]
Federal, Current	$ (339)	$ (3,728)	$ 4,652
Federal, Deferred	(1,644)	8,792	(1,386)
Federal, Total	(1,983)	5,064	3,266
State and Local, Current	73	150	1,426
State and Local, Deferred	(305)	(584)	(273)
State and Local, Total	(232)	(434)	1,153
Foreign, Current	20	13	24
Foreign, Total	20	13	24
Income tax expense (benefit)	$ (2,195)	$ 4,643	$ 4,443

Income Taxes - Reconciliation of Differences Between Federal Statutory and Effective Income (Loss) Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Income Tax Disclosure [Abstract]
U.S. federal statutory tax	21.00%	35.00%	35.00%
Computed “expected” tax expense (benefit)	$ (2,256)	$ (716)	$ 4,508
Minority interest	(87)	(105)	(89)
Permanent differences	220	96	131
State and local income taxes, net of federal income tax effect	(436)	5	673
FICA and other tax credits	(522)	(502)	(556)
Equity compensation	1,089	2,112
Adjustments	(252)	(93)	(300)
Rate change	49	3,846	76
Income tax expense (benefit)	$ (2,195)	$ 4,643	$ 4,443

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Income Tax [Line Items]
U.S. federal corporate tax rate	21.00%	35.00%	35.00%
Change in initial estimates recorded related to enactment of Tax Act	$ 0
Unrecognized tax benefits, income tax penalties and interest accrued	0	$ 0
Valuation Allowance Tax Credit Carryforward [Member]
Income Tax [Line Items]
Change in valuation allowance	$ 0	$ 0

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 30, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 576	$ 11
Accrued liabilities	1,449	842
Deferred revenue	543	120
Stock-based compensation	2,685	4,495
Property and equipment	5,037	3,258
Deferred rent	4,373	4,229
Tax credits and charitable contribution carryforwards	981	273
Other		127
Total deferred tax assets	15,644	13,355
Net deferred tax assets	15,644	13,355
Deferred tax liabilities:
Prepaids	(466)	(452)
Intangible assets	(1,075)	(977)
Smallwares	(566)	(574)
Other	(152)	(150)
Total deferred tax liabilities	(2,259)	(2,153)
Net deferred tax assets	$ 13,385	$ 11,202

Debt and Credit Facilities - Additional Information (Detail) - J P Morgan Chase Bank N A [Member] - USD ($)		12 Months Ended
	Dec. 09, 2015	Dec. 30, 2018
Minimum [Member]
Debt Instrument [Line Items]
Percentage of commitment fees based on credit facility		0.125%
Maximum [Member]
Debt Instrument [Line Items]
Percentage of commitment fees based on credit facility		0.20%
Senior Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility agreement term period	5 years
Revolving credit facility agreement expiration date	Nov. 30, 2020
Credit facility, Maximum borrowing capacity	$ 50,000,000
Credit facility, possible future maximum borrowing capacity	$ 75,000,000
Credit facility outstanding amount		$ 0
Senior Credit Facility [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.00%
Senior Credit Facility [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.75%
Senior Credit Facility [Member] \| Prime Rate [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.00%
Senior Credit Facility [Member] \| Prime Rate [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.50%

Capital Stock and Warrants - Additional Information (Detail) - USD ($)		12 Months Ended
	Jun. 30, 2017	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016	Jun. 14, 2018	May 08, 2018	Sep. 08, 2016
Capital Stock And Warrants [Line Items]
Capital stock, authorized		210,000,000	210,000,000
Common stock, authorized		200,000,000	200,000,000
Preferred stock, authorized		10,000,000	10,000,000
Common stock, issued		32,943,740	31,831,196
Common stock, outstanding		24,142,586	24,999,688
Stock repurchase program, authorized amount						$ 65,000,000
Common stock repurchased value		$ 22,916,000	$ 12,941,000	$ 22,321,000
Remaining dollar value of authorization under the share repurchase program		$ 42,100,000
Common stock, par value		$ 0.01	$ 0.01
Company warrants outstanding		0	0
Proceeds from exercise of stock warrants	$ 2,000,000		$ 1,972,000
Amended and Restated 2013 Long-Term Incentive Plan [Member]
Capital Stock And Warrants [Line Items]
Additional shares of common stock reserved for issuance					1,000,000
Common stock, par value					$ 0.01
Total number of shares registered					3,500,000
Previous Share Repurchase Program [Member]
Capital Stock And Warrants [Line Items]
Stock repurchase program, authorized amount							$ 30,000,000
Common stock shares repurchased		5,000
Common stock repurchased value		$ 100,000
New Stock Repurchase Program [Member]
Capital Stock And Warrants [Line Items]
Common stock shares repurchased		1,948,245
Common stock repurchased value		$ 22,900,000

Operating Leases - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 30, 2018 USD ($) Option	Dec. 31, 2017 USD ($)	Dec. 25, 2016 USD ($)
Operating Leased Assets [Line Items]
Initial operating lease period	10 years
Number of renewal options under operating leases \| Option	2
Operating lease rent increment term	5 years
Letters of credit in lieu of rent deposits \| $	$ 0.2	$ 0.2	$ 0.7
Letters of credit annual fee percentage	1.50%
Minimum [Member]
Operating Leased Assets [Line Items]
Operating lease period for expiration or renewal	2019
Maximum [Member]
Operating Leased Assets [Line Items]
Operating lease period for expiration or renewal	2028

Operating Leases - Schedule of Rental Expenses Under Operating Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Operating Leases Rent Expense [Abstract]
Minimum rentals	$ 46,334	$ 45,334	$ 40,252
Contingent rentals	1,295	1,408	1,755
Less: sublease rentals	0	(33)	(94)
Total	$ 47,629	$ 46,709	$ 41,913

- Definition

The increases or decreases in lease payments that result from changes occurring after the inception of the lease in the factors (other than the passage of time) on which lease payments are based, except that any escalation of minimum lease payments relating to increases in construction or acquisition cost of the leased property or for increases in some measure of cost or value during the construction or preconstruction period, are excluded from contingent rentals. Contingent rentals also may include amounts for which the triggering events have not yet occurred or the specified targets for which have not yet been achieved (such as sales based percentage rent), but which events are considered probable of occurring or which specified targets are considered probable of being achieved.

+ References + Details

Operating Leases - Schedule of Future Minimum Rental Payments Under Operating Leases (Detail) $ in Thousands	Dec. 30, 2018 USD ($)
Leases [Abstract]
2019	$ 47,918
2020	45,828
2021	41,497
2022	36,120
2023	31,060
Thereafter	138,928
Total minimum payments required	$ 341,351

Operating Leases - Schedule of Future Minimum Rental Payments Under Operating Leases (Parenthetical) (Detail) $ in Millions	Dec. 30, 2018 USD ($)
Leases [Abstract]
Minimum sublease rentals due in future	$ 1.6

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Abstract]
Contributions made to profit sharing plan	$ 0.4	$ 0.4	$ 0.4

Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Thousands	1 Months Ended							12 Months Ended
	Dec. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 $ / shares shares	May 31, 2018 $ / shares shares	Nov. 30, 2017 $ / shares shares	Aug. 31, 2017 $ / shares shares	May 31, 2017 $ / shares shares	May 31, 2016 $ / shares shares	Dec. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 25, 2016 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Recognized stock-based compensation expense \| $								$ 2,882	$ 4,676	$ 3,057
Unrecognized stock compensation expense \| $	$ 3,000							$ 3,000
Unrecognized stock compensation expense, recognition period								2022
Restricted Stock Units (RSUs) [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued	37,353	19,157	74,760		2,608	153,369	52,558
Options vesting period								3 years
Restricted stock units issued, grant-date fair value \| $ / shares	$ 9.37	$ 13.05	$ 13.25		$ 11.15	$ 11.05	$ 13.27
Vesting description								The senior leadership team grants vest in one-third increments over a three-year period.
Restricted Stock Units (RSUs) [Member] \| First Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%	50.00%	50.00%		50.00%	50.00%	50.00%
Restricted Stock Units (RSUs) [Member] \| Second Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%	50.00%	50.00%		50.00%	50.00%	50.00%
Restricted Stock Units (RSUs) One [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued				6,848
Restricted stock units issued, grant-date fair value \| $ / shares				$ 11.50
Restricted Stock Units (RSUs) One [Member] \| First Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				50.00%
Restricted Stock Units (RSUs) One [Member] \| Second Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				50.00%
Restricted Stock Units (RSUs) Two [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued				78,125
Restricted stock units issued, grant-date fair value \| $ / shares				$ 12.80
Restricted Stock Units (RSUs) Two [Member] \| First Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				50.00%
Restricted Stock Units (RSUs) Two [Member] \| Second Anniversary [Member] \| Non-Employee Board Of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage				50.00%
2013 Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	2,514,194							2,514,194
Shares of common stock reserved for issuance	1,699,387							1,699,387
Restricted stock units granted against shares reserved for future issuance ratio			2
Exercise price of options outstanding, lower limit \| $ / shares								$ 7.00
Exercise price of options outstanding, higher limit \| $ / shares								$ 20.53
2013 Long Term Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period from the date of grant								10 years
Options issued and outstanding, last expiration date								Dec. 31, 2028
Options vesting period								5 years
2013 Long Term Incentive Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period								4 years
2013 Long Term Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock								28,240
2013 Long Term Incentive Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued								460,855

Stock-Based Compensation - Summary of Stock Options Activity Under Plans and Agreement (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding shares, beginning balance	3,309	4,013	4,368
Options, granted	203	464	369
Options, exercised	(993)	(653)	(536)
Options, canceled	(369)	(515)	(188)
Options outstanding shares, ending balance	2,150	3,309	4,013	4,368
Options outstanding shares, exercisable	1,611
Options outstanding weighted average exercise price, beginning balance	$ 10.71	$ 10.61	$ 10.53
Options, weighted average exercise price, granted	11.27	12.09	13.65
Options, weighted average exercise price, exercised	8.30	9.94	10.77
Options, weighted average exercise price, canceled	13.63	12.18	14.40
Options outstanding weighted average exercise price, ending balance	11.49	$ 10.71	$ 10.61	$ 10.53
Options outstanding weighted average exercise price, exercisable	$ 11.14
Options outstanding aggregate intrinsic value	$ 378	$ 7,699	$ 13,455	$ 9,742
Options exercisable aggregate intrinsic value	$ 378
Option outstanding weighted average remaining term	5 years 1 month 17 days	4 years 10 months 24 days	4 years 9 months 10 days	5 years 1 month 6 days
Options exercisable weighted average remaining term	4 years 6 months 7 days

Stock-Based Compensation - Schedule of Average Assumptions to Value Options (Detail) - $ / shares	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Risk-free interest rate	3.00%	2.00%	1.70%
Expected life (years)	6 years 3 months	6 years 3 months	7 years
Expected dividend yield	0.00%	0.00%	0.00%
Volatility	35.00%	36.00%	49.40%
Weighted average grant date fair value	$ 4.52	$ 4.76	$ 7.05

Quarterly Financial Data (Unaudited) - Summary of Unaudited Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 102,378	$ 106,996	$ 110,347	$ 102,917	$ 112,149	$ 106,127	$ 108,136	$ 101,699	$ 422,638	$ 428,111	$ 407,131
Income (loss) from operations	(5,370)	(2,697)	95	(2,630)	(2,776)	(574)	164	1,263	(10,602)	(1,923)	13,013
Net income (loss) attributable to Potbelly Corporation	$ (4,363)	$ (1,961)	$ (360)	$ (2,194)	$ (7,261)	$ (240)	$ (138)	$ 683	$ (8,878)	$ (6,956)	$ 8,212
Income (loss) per share available to common stockholders-basic	$ (0.17)	$ (0.08)	$ (0.01)	$ (0.09)	$ (0.29)	$ (0.01)	$ (0.01)	$ 0.03	$ (0.35)	$ (0.28)	$ 0.32
Income (loss) per share available to common stockholders-diluted	$ (0.17)	$ (0.08)	$ (0.01)	$ (0.09)	$ (0.29)	$ (0.01)	$ (0.01)	$ 0.03	$ (0.35)	$ (0.28)	$ 0.31

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Commitment and Contingencies - Additional Information (Detail)	1 Months Ended
	Oct. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Purported collective and class action lawsuit filed date	October 2017

Revenue - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
Revenue - Additional Information (Detail) - USD ($)	Dec. 30, 2018	Sep. 30, 2018	Jul. 01, 2018	Apr. 01, 2018	Dec. 31, 2017	Sep. 24, 2017	Jun. 25, 2017	Mar. 26, 2017	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Disaggregation Of Revenue [Line Items]
Amount of revenue recognized	$ 102,378,000	$ 106,996,000	$ 110,347,000	$ 102,917,000	$ 112,149,000	$ 106,127,000	$ 108,136,000	$ 101,699,000	$ 422,638,000	$ 428,111,000	$ 407,131,000
Aggregate value of remaining performance obligation on outstanding contracts	$ 3,815,000								3,815,000
Revenue recognized related to prior periods									0
January 1, 2018 Liability Ending Balance [Member]
Disaggregation Of Revenue [Line Items]
Amount of revenue recognized									2,100,000
Point in Time Sales [Member]
Disaggregation Of Revenue [Line Items]
Amount of revenue recognized									421,800,000
Over Time Sales [Member]
Disaggregation Of Revenue [Line Items]
Amount of revenue recognized									$ 800,000

Revenue - Summary of Current and Noncurrent Contract Liabilities from Contracts with Customers (Detail) $ in Thousands	12 Months Ended
	Dec. 30, 2018 USD ($)
Revenue From Contract With Customer [Abstract]
Beginning balance of current contract liability	$ (2,325)
Ending balance of current contract liability	(2,184)
Decrease in contract liability, current	(141)
Beginning balance of noncurrent contract liability	(2,144)
Ending balance of noncurrent contract liability	(1,631)
Decrease in contract liability, noncurrent	$ (513)

Revenue - Summary of Expected Revenue Recognition Related to Contract Liabilities (Detail1) $ in Thousands	Dec. 30, 2018 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 3,815
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 2,184
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 199
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 195
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 189
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 501
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligations	$ 547
Revenue, remaining performance obligation, expected timing of satisfaction, period

Revenue - Summary of Expected Revenue Recognition Related to Contract Liabilities (Detail) $ in Thousands	Dec. 30, 2018 USD ($)
Revenue From Contract With Customer [Abstract]
Revenue, remaining performance obligations	$ 3,815