Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)		3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 30, 2014	Dec. 25, 2019 USD ($)	Sep. 25, 2019 USD ($) restaurant shares	Sep. 26, 2018 USD ($) restaurant	Sep. 25, 2019 USD ($) restaurant supplier segment shares	Sep. 26, 2018 USD ($) restaurant	Dec. 27, 2017 USD ($) supplier	Oct. 29, 2019 restaurant	Sep. 25, 2019	Sep. 25, 2019 USD ($)	May 17, 2019 USD ($)	Dec. 26, 2018 USD ($)	Aug. 28, 2018 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net										$ 93,364,000		$ 104,145,000
Depreciation				$ 4,500,000	$ 13,600,000	$ 13,100,000
Number of operating segments | segment					1
Treasury Stock, Value, Acquired, Cost Method			$ 29,938,000		$ (48,264,000)
Total amount of outstanding debt										101,000,000
Cash available				8,142,000		8,142,000	$ 8,550,000			12,069,000		6,969,000
Recovery of securities lawsuits related legal expenses			0	(2,036,000)	(10,000,000)	(6,099,000)
Proceeds from Divestiture of Businesses					4,770,000	0
Gain (Loss) on Disposition of Business			(11,000)	0	(5,062,000)	0
Proceeds from Long-term Lines of Credit					42,000,000	6,307,000
Asset Impairment Charges			56,000	84,000	283,000	1,791,000
Closed-store reserve expense (recovery)				(200,000)	0	4,838,000
Unrecognized tax benefits, accrual of interest or penalties										0		$ 0
Unrecognized tax benefits, interest or penalties expenses			0	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%
Income tax receivable agreement income			(197,000)	$ (571,000)	$ (120,000)	$ (777,000)
Stock Repurchase Program Expiration Date					Mar. 25, 2020
Indefinite-lived Intangible Assets
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Asset Impairment Charges			$ 0
Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of suppliers | supplier					2		1
Supplier Concentration Risk | Supplier One | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration					14.60%		36.00%
Supplier Concentration Risk | Supplier Two | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration					10.20%
Supplier Concentration Risk | Largest Supplier One | Purchased
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration			29.00%	29.40%	28.90%	28.80%
Geographic Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration			100.00%	100.00%	100.00%	100.00%
Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				$ 0		$ 0				0
Property and equipment owned, net										171,000
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				0		0				0
Property and equipment owned, net										0
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				0		0				0
Property and equipment owned, net										171,000
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				$ 0		$ 0				0
Property and equipment owned, net										$ 0
Los Angeles | Geographic Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration			71.50%	69.30%	70.00%	69.00%
TEXAS
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants closed			1			6
TEXAS | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants								5
Closed-store reserve expense (recovery)		$ 800,000
ARIZONA
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants				1		1			7
Number of restaurants closed				1
CALIFORNIA
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants			1		1				4
Number of restaurants closed			1	1
closed store [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Expense			$ 300,000		$ 1,000,000
Common Stock [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Treasury Stock, Shares, Acquired | shares					(4,384,732)
Treasury Stock, Value, Acquired, Cost Method			(28,000)		$ 43,000
Additional Paid-in Capital [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Treasury Stock, Value, Acquired, Cost Method			$ (29,910,000)		$ 48,221,000
Entity Operated Units
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant			201		201
Franchised Units
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant			284		284
2019 Stock Repurchase Plan [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Stock Repurchase Program, Authorized Amount											$ 30,000,000
2019 Stock Repurchase Plan [Member] | Common Stock [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Treasury Stock, Shares, Acquired | shares			(2,825,896)
2018 Stock Repurchase Plan [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Stock Repurchase Program, Authorized Amount													$ 20,000,000
2018 Stock Repurchase Plan [Member] | Additional Paid-in Capital [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Treasury Stock, Shares, Acquired | shares					(1,558,836)
Company Operated Properties [Member] | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant								1