Summary of Significant Accounting Policies - Additional Information (Details)				1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended
	Jul. 13, 2018 USD ($)	Jul. 30, 2014	Jul. 11, 2014 restaurant	Nov. 30, 2015 restaurant	Mar. 08, 2019 USD ($)	Sep. 27, 2017 restaurant	Dec. 26, 2018 USD ($) restaurant franchise	Dec. 27, 2017 USD ($) restaurant	Dec. 28, 2016 USD ($) restaurant	Jan. 31, 2019 restaurant	Sep. 26, 2018 restaurant	Jun. 27, 2018 restaurant	Mar. 28, 2018 restaurant	Dec. 28, 2017 USD ($)	Jun. 28, 2017 restaurant	Mar. 29, 2017 restaurant	Dec. 30, 2015 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Total amount of outstanding debt							$ 74,200,000
Cash available							6,969,000	$ 8,550,000	$ 2,168,000								$ 6,101,000
Capitalized internal cost							1,300,000	1,900,000	1,600,000
Capitalized internal interest cost							200,000	200,000	200,000
Asset impairment charges							$ 5,147,000	$ 32,594,000	$ 8,400,000
Number of restaurants | restaurant							4	23	9
Transaction costs	$ 800,000
Amortization expense for deferred financing costs							$ 280,000	$ 304,000	$ 304,000
Accrued insurance							7,076,000	5,851,000
Expense for payroll and benefits reserves							8,000,000	6,800,000	7,200,000
Promotional allowances amount							8,800,000	8,900,000	7,400,000
Revenue allocated to loyalty points not redeemed							$ 1,000,000	400,000
Loyalty rewards program, expected loyalty points redemption period							1 year
Advertising expense							$ 16,100,000	15,500,000	14,700,000
Accrued advertising							300,000	1,000,000
Advertising cost included in accounts receivable and current assets							0	0
Number of restaurants damaged by fire | restaurant				1
Expenses related to fire loss									100,000
Disposition of assets related to fire									100,000
Gain on recovery of insurance proceeds, related to the reimbursement of property and equipment and expenses incurred									700,000
Gain on recovery of insurance proceeds, related to the reimbursement of lost profits							0	0	502,000
Amount received from insurance company in cash									1,400,000
Recovery of securities lawsuits related legal expenses							8,356,000	1,666,000	0
Unrecognized tax benefits, accrual of interest or penalties							0	0
Unrecognized tax benefits, interest or penalties expenses							0	0	0
Percentage of cash savings in taxes realized as a result of utilizing net operating losses payable to pre-IPO stockholders		85.00%
Charge relating to present value of total expected TRA payments							13,900,000	22,000,000
Payments to pre-IPO stockholders under TRA							$ 7,272,000	$ 11,109,000	3,236,000
Number of restaurants that failed impairment testing | restaurant							4	21
Number of commitments to open franchised restaurants | franchise							44
Operating lease obligations							$ 266,481,000
Minimum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of monthly franchise fee							4.00%
Maximum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of monthly franchise fee							5.00%
Franchised
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant						265	271	265			271	269	268		264	263
Advertising fees							$ 21,200,000	$ 20,500,000	19,300,000
Interest Expense
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amortization expense for 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							300,000	500,000	500,000
Preopening costs							800,000	2,000,000	$ 2,600,000
Other Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Deferred financing fees net of accumulated amortization							$ 1,100,000	$ 600,000
Revenue | Geographic Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration							100.00%
Accounts Receivable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration						40.00%	40.00%
Supplier One | Accounts Payable | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration							36.00%
Supplier Two | Accounts Payable | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration								14.00%
Largest Supplier One | Purchased | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration							29.00%	29.00%	33.00%
Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants closed | restaurant								2
Asset impairment charges								$ 27,700,000
Greater Los Angeles area market | Franchised
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant							138
Greater Los Angeles area market | Revenue | Geographic Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration							69.20%	73.00%	75.00%
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 | 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			10 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
First Lien Credit Agreement | Senior Secured Revolving Credit Facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amount of borrowings available							$ 67,500,000
2018 Credit Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amount of borrowings available							67,500,000
Accounting Standards Update 2014-09
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of adjustment resulted in an increase in accumulated deficit														$ (3,467,000)
Retained Earnings | Accounting Standards Update 2014-09
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of adjustment resulted in an increase in accumulated deficit														$ (3,467,000)
Cumulative effect adjustment as percentage of total assets														(0.77006%)
Subsequent Event | Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants closed | restaurant										1
Subsequent Event | 2018 Credit Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Prepayment for long-term line of credit					$ 3,000,000
Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Impairment of assets							$ 5,147,000	$ 32,594,000	$ 8,400,000