Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 27, 2017		Sep. 27, 2017		Jun. 28, 2017		Mar. 29, 2017		Dec. 28, 2016		Sep. 28, 2016		Jun. 29, 2016		Mar. 30, 2016		Dec. 27, 2017	Dec. 28, 2016	Dec. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Company restaurant sales	$ 100,303		$ 97,915		$ 98,355		$ 93,779		$ 94,592		$ 93,122		$ 89,210		$ 90,386		$ 390,352	$ 367,310	$ 353,073
Franchise and licensing revenue	35,196		34,469		35,021		34,131		35,013		35,264		35,105		34,256		138,817	139,638	138,220
Total operating revenue	135,499		132,384		133,376		127,910		129,605		128,386		124,315		124,642		529,169	506,948	491,293
Total operating costs and expenses	116,646		113,849		116,367		111,609		113,583		110,809		129,148		106,409		458,471	459,949	428,142
Operating income	18,853		18,535		17,009		16,301		16,022		17,577		(4,833)		18,233		70,698	46,999	63,151
Net income	$ 13,147		$ 9,325		$ 8,749		$ 8,373		$ 11,274		$ 9,726		$ (11,552)		$ 9,954		$ 39,594	$ 19,402	$ 35,976
Basic net income per share	$ 0.20	[1]	$ 0.14	[1]	$ 0.13	[1]	$ 0.12	[1]	$ 0.16	[2]	$ 0.13	[2]	$ (0.15)	[2]	$ 0.13	[2]	$ 0.58	$ 0.26	$ 0.44
Diluted net income per share	$ 0.19	[1]	$ 0.13	[1]	$ 0.12	[1]	$ 0.11	[1]	$ 0.15	[2]	$ 0.13	[2]	$ (0.15)	[2]	$ 0.13	[2]	$ 0.56	$ 0.25	$ 0.42

[1] Per share amounts do not necessarily sum to the total year amounts due to changes in shares outstanding and rounding

[2] Per share amounts do not necessarily sum to the total year amounts due to changes in shares outstanding and rounding.