Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)			3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 25, 2020 USD ($) restaurant	Jul. 30, 2014	Jun. 24, 2020 USD ($) restaurant	Jun. 26, 2019 USD ($) restaurant	Jun. 24, 2020 USD ($) restaurant segment item	Jun. 26, 2019 USD ($) restaurant	Dec. 25, 2019 USD ($)
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Historical dine-in percentage					20.00%
Number of Restaurants Permanently Closed | restaurant			0		0
Deferred April royalties percentage					50.00%
Deferred 2020 remodel and new restaurant build requirements percentage					100.00%
Repayments of Lines of Credit					$ 10,700,000	$ 15,000,000
Property and equipment owned, net			$ 84,262,000		$ 84,262,000		$ 91,778,000
Number of operating segments | segment					1
Impairment of property and equipment			52,000	$ 227,000	$ 1,429,000	227,000
Impairment of Right-of-Use Assets					543,000
Asset Impairment Charges			100,000	200,000	1,972,000	227,000
Total amount of outstanding debt			138,800,000		138,800,000
Cash available			60,342,000		60,342,000		8,070,000
Insurance proceeds			100,000	10,000,000.0	100,000	10,000,000.0
Assets Held-for-sale, Not Part of Disposal Group, Current			0		0
Unrecognized tax benefits, accrual of interest or penalties			0		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%
Tax Receivable Agreement (Income) Expenses			290,000	(94,000)	170,000	77,000
AMT Credits, CARES Act			$ 400,000		$ 400,000
Proceeds from disposition of restaurants						4,770,000
Loss on disposition of restaurants				$ (927,000)		$ (5,051,000)
Supplier Concentration Risk
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number Of Suppliers | item					1
Supplier Concentration Risk | Supplier One | Accounts Payable
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration					44.50%		11.70%
Supplier Concentration Risk | Largest Supplier One | Purchased
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration			26.40%	30.30%	27.00%	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%
Subsequent Event | Letter of Credit
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Letter of credit released	$ 2,700,000
Fair Value, Measurements, Recurring [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative Liability, Fair Value, Gross Liability			$ 1,408,000		$ 1,408,000
Derivative Liability, Fair Value, Gross Asset							$ 360,000
Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				$ 0		$ 0
Right-of-Use Assets, Net			918,000		918,000
Level 1 | Fair Value, Measurements, Recurring [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative Liability, Fair Value, Gross Liability			0		0
Derivative Liability, Fair Value, Gross Asset							0
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	0
Right-of-Use Assets, Net			0		0
Level 2 | Fair Value, Measurements, Recurring [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative Liability, Fair Value, Gross Liability			1,408,000		1,408,000
Derivative Liability, Fair Value, Gross Asset							360,000
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	0
Right-of-Use Assets, Net			0		0
Level 3 | Fair Value, Measurements, Recurring [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative Liability, Fair Value, Gross Liability			0		0
Derivative Liability, Fair Value, Gross Asset							$ 0
Level 3 | Fair Value, Measurements, Nonrecurring
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Property and equipment owned, net				$ 0		$ 0
Right-of-Use Assets, Net			$ 918,000		$ 918,000
Texas
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant			1		1
Number of restaurants closed | restaurant				1		1
Houston
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants fully open | restaurant					9
Utah
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants fully open | restaurant					1
California
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of restaurants | restaurant			3	1	3	1
Impairment of property and equipment			$ 100,000	$ 200,000	$ 1,400,000	$ 200,000
Number of restaurants closed | restaurant				1		1
Greater Los Angeles area market | Geographic Concentration Risk | Revenue
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration			71.10%	69.30%	71.70%	69.30%
Closed Store
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Closed-store reserve expense			$ 400,000	$ 300,000	$ 900,000	$ 600,000
Company-operated
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Temporary Closed | restaurant			31		31
Number of Restaurants Reopened | restaurant			30		30
Number of Restaurants Remain Closed | restaurant			1		1
Number of restaurants | restaurant			196		196
Proceeds from disposition of restaurants						4,800,000
Loss on disposition of restaurants				$ (900,000)		$ (5,100,000)
Company-operated | Minimum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Temporary closure period					1 day
Company-operated | Maximum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Temporary closure period					3 days
Company-operated | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Temporary Closed | restaurant	36
Number of Restaurants Remain Closed | restaurant	4
Company-operated | Subsequent Event | Minimum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Temporary closure period	1 day
Company-operated | Subsequent Event | Maximum
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Temporary closure period	3 days
Company-operated | San Francisco
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Sold | restaurant				4		4
Company-operated | Phoenix
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Sold | restaurant				7		7
Franchised
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Temporary Closed | restaurant			21		21
Number of Restaurants Reopened | restaurant			17		17
Number of Restaurants Remain Closed | restaurant			4		4
Number of restaurants | restaurant			283		283
Franchised | Subsequent Event
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of Restaurants Temporary Closed | restaurant	11
Number of Restaurants Remain Closed | restaurant	3