Summary of Significant Accounting Policies - Additional Information (Detail)			1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Jul. 30, 2014	Jul. 11, 2014 restaurant	Nov. 30, 2015 restaurant	Mar. 09, 2018 USD ($) restaurant franchise store shares	Mar. 28, 2018 USD ($)	Dec. 27, 2017 USD ($) restaurant	Dec. 28, 2016 USD ($) restaurant	Dec. 30, 2015 USD ($) restaurant	Sep. 27, 2017 restaurant	Jun. 28, 2017 restaurant	Mar. 29, 2017 restaurant	Jan. 17, 2017 USD ($)	Sep. 28, 2016 restaurant	Jun. 29, 2016 restaurant	Mar. 30, 2016 restaurant	Dec. 31, 2014 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Total amount of outstanding debt						$ 93,300,000
Cash available						8,550,000	$ 2,168,000	$ 6,101,000								$ 11,499,000
Expected closed-store reserve						1,051,000	154,000	(89,000)
Capitalized internal cost						1,900,000	1,600,000	1,100,000
Capitalized internal interest cost						200,000	200,000
Amortization expense for deferred financing costs						304,000	304,000	304,000
Asset impairment charges						32,594,000	8,400,000	181,000
Accrued insurance						5,851,000	5,444,000
Expense for payroll and benefits reserves						6,800,000	7,200,000	7,900,000
Promotional allowances amount						8,900,000	7,400,000	7,400,000
Initial franchise revenue						$ 300,000	400,000	800,000
Number of commitments to open franchised restaurants | restaurant						55
Advertising expense						$ 15,500,000	14,700,000	13,900,000
Accrued advertising						1,000,000	0
Advertising cost included in accounts receivable and current assets						0	100,000
Number of restaurants damaged by fire | restaurant			1
Costs incurred directly related to fire (less than $0.1 million)						0	48,000	0
Disposition of assets related to fire							100,000	100,000
Gain on recovery of insurance proceeds, related to the reimbursement of property and equipment and expenses incurred						0	741,000	0
Gain on recovery of insurance proceeds, related to the reimbursement of lost profits						0	502,000	0
Amount received from insurance company in cash							1,400,000
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						22,000,000		41,400,000
Payments to pre-IPO stockholders under TRA						11,109,000	3,236,000	0
Future minimum payments due						298,147,000
Recovery of securities lawsuits related legal expenses						$ 1,666,000	$ 0	0
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	259		265	264	263		253	251	248
Advertising fees						$ 20,500,000	$ 19,300,000	18,500,000
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						500,000	500,000	100,000
Preopening costs						2,000,000	2,600,000	1,500,000
Other Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Deferred financing fees net of accumulated amortization						600,000	900,000
Indefinite-lived Intangible Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Asset impairment charges						$ 0	$ 0	$ 0
Number of restaurants | restaurant						23	9	1
Number of restaurants that failed impairment testing | restaurant						21
Supplier One | Accounts Payable | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration						14.20%
Supplier Two | Accounts Payable | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration							16.00%
Largest Supplier One | Purchased | Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration						29.30%	33.00%	36.00%
Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurant closed | restaurant						2
Asset impairment charges						$ 27,700,000
California | Indefinite-lived Intangible Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant								1
Los Angeles | Franchised
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant						138
Los Angeles | Revenue | Geographic Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration						73.00%	75.00%	79.00%
Senior Secured Revolving Credit Facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Pre-payment for new restaurant												$ 1,500,000
Development
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Unrecognized area development fees						$ 1,000,000	$ 900,000
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 | 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
Related party agreement, termination description						The Franchise Development Option Agreement terminates (i) ten years after execution, or (ii) if the Initial Option is exercised, five years after that exercise.
First Lien Credit Agreement | Senior Secured Revolving Credit Facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amount of borrowings available						$ 99,300,000
2014 Credit Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amount of borrowings available						99,300,000
Subsequent Events
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Amount received from insurance company in cash				$ 1,600,000
Subsequent Events | Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurant closed | restaurant				2
Number of restaurants closed or development ceased | restaurant				3
Subsequent Events | Parent
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of new stores opened | store				1
Subsequent Events | Franchisees
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of new stores opened | franchise				2
Subsequent Events | 2014 Credit Agreement
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Repayments of debt				$ 8,000,000
Accounting Standards Update 2016-02
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Future minimum payments due						$ 298,100,000
Accounting Standards Update 2015-07
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Deferred tax assets reclassified to noncurrent							21,500,000
Deferred tax assets reclassified from current							$ 21,500,000
Accounting Standards Update 2014-09
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Expected percentage of total assets						1.00%
Retained Earnings | Accounting Standards Update 2014-09
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cumulative effect on retained earnings						$ 3,500,000
Forecast | Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Expected closed-store reserve					$ 3,000,000
Stock Options | Subsequent Events
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accelerated vesting (shares) | shares				33,545