Acquisition (Details)	3 Months Ended		9 Months Ended		12 Months Ended	15 Months Ended
	Sep. 30, 2018 USD ($)	Oct. 01, 2017 USD ($)	Sep. 30, 2018 USD ($)	Oct. 01, 2017 USD ($)	Dec. 31, 2017 USD ($)	Apr. 01, 2018 USD ($)
Business Acquisition [Line Items]
Right of First Refusal, Number of States	20		20
Number of Restaurants Acquired						98
Business acquisitions, purchase price			$ 27,595,000	$ 36,556,000		$ 65,518,000
Proceeds from sale-leaseback transactions			4,504,000	4,257,000
Restaurant sales	$ 296,917,000	$ 285,235,000	871,553,000	$ 804,565,000
Goodwill	38,053,000		$ 38,053,000		$ 36,792,000
November 17, 2015 Acquisition 2 [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired			1
Business acquisitions, purchase price			$ 0
Franchise rights	290,000		290,000
Liabilities assumed in excess of consideration	230,000		230,000
2018 Acquisitions [Member]
Business Acquisition [Line Items]
Goodwill	1,261,000		1,261,000
February 28, 2017 Acquisition [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired				43
Business acquisitions, purchase price				$ 20,366,000
June 6, 2017 Acquisition [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired				17
Business acquisitions, purchase price				$ 16,355,000
Acquired Restaurants [Member]
Business Acquisition [Line Items]
Restaurant sales	$ 25,600,000	$ 22,000,000	$ 71,200,000	$ 42,600,000
October 1, 2015 Acquisition [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired					4
Business acquisitions, purchase price					$ 1,202,000
October 20, 2015 Acquisition [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired					64
Business acquisitions, purchase price					$ 37,923,000
August 21, 2018 Acquisition 2 [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired			2
Business acquisitions, purchase price			$ 1,666,000
September 5, 2018 Acquisition 2 [Member]
Business Acquisition [Line Items]
Number of Restaurants Acquired			31
Business acquisitions, purchase price			$ 25,929,000