Summary of Significant Accounting Policies - Additional Information (Details)								1 Months Ended	12 Months Ended
	Mar. 12, 2021 USD ($)	Dec. 31, 2020 USD ($)	Aug. 04, 2020 USD ($) item	Aug. 03, 2020 USD ($) item	Jul. 13, 2018 USD ($)	Jul. 30, 2014	Jul. 11, 2014 restaurant	Apr. 30, 2020	Dec. 30, 2020 USD ($) restaurant item segment	Dec. 25, 2019 USD ($) item	Dec. 26, 2018 USD ($) restaurant	Jan. 02, 2018 USD ($)	Jan. 06, 2015 USD ($)	Dec. 25, 2019 restaurant	Dec. 25, 2019	Dec. 27, 2017 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | segment									1
Historical dine-in percentage									20.00%
Leaves of absence and overtime pay due to COVID 19									$ 4,900,000
Franchisee royalties deferred percentage								50.00%
Franchisee remodel and new restaurant build requirements deferral percentage								100.00%
Repayments of Lines of Credit									93,700,000	$ 19,000,000	$ 33,000,000
Revolving line of credit									62,800,000	97,000,000
Bad debt expense									190,000	0	0
Total amount of outstanding debt									62,800,000
Cash available									13,219,000	8,070,000
Gain on recovery of insurance proceeds									2,000,000	0	0
Insurance proceeds									100,000
Number of Restaurants Sold | restaurant														4
Proceeds from disposition of restaurants									0	4,770,000	0
Loss on disposition of restaurants									0	(5,058,000)	0
Amortization of deferred financing costs									252,000	251,000	280,000
Accounts payable									7,472,000	5,627,000
Operating Lease ROU assets									177,129,000	192,395,000
Asset Impairment Charges									3,498,000	3,559,000	5,147,000
Closed-store reserve expense									0	0	$ 4,503,000
Number of restaurants closed | restaurant											7			1
Unrecognized tax benefits, accrual of interest or penalties									0	0
Interest related to NOPA									100,000
TRA tax expense (benefit)									100,000	100,000	$ (800,000)	$ (5,600,000)	$ 41,400,000
Percentage of cash savings in taxes realized as a result of utilizing net operating losses payable to pre-IPO stockholders						85.00%
Tax Receivable Agreement (Income) Expenses									139,000	57,000	(761,000)
AMT Credits, CARES Act									400,000
Capitalized internal cost									1,000,000.0	1,100,000	1,300,000
Capitalized internal interest cost									100,000	100,000	200,000
Transaction costs					$ 800,000
Expense for payroll and benefits reserves									8,400,000	9,600,000	8,000,000.0
Promotional allowances amount									$ 7,500,000	8,000,000.0	8,800,000
Loyalty Rewards Program, Points Needed For One Reward | item			50	100
Loyalty Rewards Program, Award Earned			$ 5	$ 10
Loyalty Rewards Program, Expiration Period For Inactivity			1 year
Loyalty Reward Program, unused reward expiration period			6 months
Loyalty Rewards Program, Expected Loyalty Points Redemption Period									1 year
Advertising expense									$ 15,300,000	16,100,000	16,100,000
Accrued advertising									100,000	500,000
Charge relating to present value of total expected TRA payments									3,200,000	8,200,000
Payments to pre-IPO stockholders under TRA									$ 5,237,000	5,764,000	7,272,000
Number of commitments to open franchised restaurants | restaurant									48
Accrued loyalty rewards program liability									$ 900,000	1,100,000
Stockholders' equity									$ 277,578,000	245,566,000	$ 265,236,000					$ 274,950,000
Cumulative Effect, Period of Adoption, Adjustment
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity																(3,467,000)
Minimum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Typical restaurant closure period									1 day
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period									10 years
Percentage of monthly franchise fee									4.00%
Maximum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Typical restaurant closure period									3 days
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period									20 years
Percentage of monthly franchise fee									5.00%
Other Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Deferred financing fees net of accumulated amortization									$ 600,000	800,000
Franchise Development Initial Option Agreement | Limited Liability Company
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant							15
Number of years available under plan							5 years
Franchise Development Additional Option Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of years available under plan							10 years
Franchise Development Additional Option Agreement | Limited Liability Company
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant							100
Number of years available under plan							5 years
Franchise Development Agreement | Limited Liability Company
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Related party agreement, termination period							10 years
Accounting Standards Update 2014-09 | Cumulative Effect, Period of Adoption, Adjustment
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity																$ 3,500,000
Closed Or Subleased Restaurant Locations
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Operating Lease ROU assets									$ 27,700,000	$ 31,800,000
Accounts Receivable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									11.50%	10.00%
Number of Franchisees | item									1	1
Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number Of Suppliers									2	1
Supplier Concentration Risk | Supplier One | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									24.20%
Supplier Concentration Risk | Supplier Two | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									11.40%	11.70%
Supplier Concentration Risk | Largest Supplier One | Purchased
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									26.90%	29.00%	28.80%
Supplier Concentration Risk | Largest Supplier One | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accounts payable									$ 0	$ 0
Geographic Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									100.00%	100.00%	100.00%
2018 Credit Agreement | Revolving Credit Facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Repayments of Lines of Credit									$ 34,200,000	$ 19,000,000.0
Line of Credit Facility, Maximum Borrowing Capacity					$ 150,000,000.0
Revolving line of credit									62,800,000	97,000,000.0
Amount of borrowings available									$ 78,800,000	$ 44,600,000
2018 Credit Agreement | Revolving Credit Facility | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Repayments of Lines of Credit		$ 7,000,000.0
Revolving line of credit	$ 55,800,000
Amount of borrowings available	85,800,000
2018 Credit Agreement | Letter of Credit | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity, Increase	1,600,000
Line of Credit Facility, Maximum Borrowing Capacity	$ 9,900,000
Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant									1
Number of Restaurants Sold | restaurant														5
Number of restaurants closed | restaurant														2
California
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants									4					1	4
Number of Restaurants Sold | restaurant											4			4
Number of restaurants closed | restaurant														2
Greater Los Angeles area market | Geographic Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration									71.30%	70.50%	69.20%
Phoenix
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Sold | restaurant														7
Interest Expense
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amortization of deferred financing costs									$ 300,000	$ 300,000	$ 300,000
General and Administrative Expense
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Abandoned site and other site selection costs									100,000	100,000	300,000
Preopening costs									100,000	400,000	800,000
Closed Store
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Closed-store reserve expense									$ 1,200,000	1,300,000
Company-operated
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant									196
Number of Restaurants Temporary Closed | restaurant									154
Number of Restaurants Remain Closed | restaurant									7
Proceeds from disposition of restaurants										4,800,000
Loss on disposition of restaurants									$ 5,100,000
Company-operated | Greater Los Angeles area market
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant									143
Franchised
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant									283
Number of Restaurants Temporary Closed | restaurant									69
Number of Restaurants Remain Closed | restaurant									3
Advertising fees									$ 22,600,000	$ 22,400,000	$ 21,200,000
Franchised | Greater Los Angeles area market
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant									136