Debt (Details)				9 Months Ended	12 Months Ended
	Dec. 10, 2015 USD ($)	Jun. 19, 2014 USD ($)	Dec. 28, 2011 USD ($)	Sep. 28, 2018	Dec. 26, 2017	Dec. 27, 2016 USD ($)	Dec. 29, 2015 USD ($)	Dec. 30, 2014 USD ($)	Jul. 14, 2014 unit
Line Of Credit Facility [Line Items]
Issuance of debt		$ 40,000,000				$ 0	$ 0	$ 40,000,000
Maximum leverage ratio						600.00%
Quarterly amortization of term loan						$ 1,000,000
Commitment fee percentage						0.50%
Number of restaurants acquired | unit									56
Senior note redemption percentage one						105.25%
Senior note redemption percentage two						102.625%
Credit agreement period						95 days
Credit agreement, prepayment amount						$ 3,300,000
Scenario, Forecast
Line Of Credit Facility [Line Items]
Maximum leverage ratio				525.00%	575.00%
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity available under our revolving line of credit			$ 110,000,000
Weighted average interest rate						4.51%
Increase to borrowing capacity of Revolving Facility			110,000,000.0
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line Of Credit Facility [Line Items]
Line of credit facility basis of spread on base rate	3.75%					3.75%
Basis of spread on base rate change						0.50%
Revolving Credit Facility
Line Of Credit Facility [Line Items]
Borrowing capacity available under our revolving line of credit						$ 80,400,000	80,900,000
Outstanding letters of credit						$ 29,600,000	$ 29,100,000
Term Loan
Line Of Credit Facility [Line Items]
Term loan borrowings			$ 375,000,000.0
Issuance of debt		40,000,000
Line of credit facility basis of spread on base rate						1.00%
Weighted average interest rate						4.75%
Term Loan | London Interbank Offered Rate (LIBOR)
Line Of Credit Facility [Line Items]
Line of credit facility basis of spread on base rate	0.75%
Basis of spread on base rate change	3.75%
Line of Credit
Line Of Credit Facility [Line Items]
Debt issuance cost	$ 1,800,000	700,000
Long-term debt
Line Of Credit Facility [Line Items]
Issuance of debt		40,000,000.0
Increase to borrowing capacity of Revolving Facility		125,000,000.0
Line of credit facility, remaining borrowing capacity		$ 85,000,000.0
Senior Notes
Line Of Credit Facility [Line Items]
Interest on senior notes						10.50%