Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 26, 2018		Sep. 26, 2018		Jun. 27, 2018		Mar. 28, 2018		Dec. 27, 2017		Sep. 27, 2017		Jun. 28, 2017		Mar. 29, 2017		Dec. 26, 2018	Dec. 27, 2017		Dec. 28, 2016
Revenue from contract with customer, excluding assessed tax	$ 159,549	[1]	$ 158,023	[1]	$ 157,334	[1]	$ 155,273	[1]	$ 135,499		$ 132,384		$ 133,376		$ 127,910		$ 630,179	$ 529,169	[2]	$ 506,948	[2]
Total operating costs and expenses, net	139,789		139,554		138,374		138,848		116,646		113,849		116,367		111,609		556,565	458,471		459,949
Operating income	19,760		18,469		18,960		16,425		18,853		18,535		17,009		16,301		73,614	70,698		46,999
Net income	$ 11,503		$ 10,805		$ 11,626		$ 9,759		$ 13,147		$ 9,325		$ 8,749		$ 8,373		$ 43,693	$ 39,594		$ 19,402
Basic net income per share	$ 0.19	[3]	$ 0.17	[3]	$ 0.18	[3]	$ 0.15	[3]	$ 0.20	[4]	$ 0.14	[4]	$ 0.13	[4]	$ 0.12	[4]	$ 0.69	$ 0.58		$ 0.26
Diluted net income per share	$ 0.18	[3]	$ 0.16	[3]	$ 0.18	[3]	$ 0.15	[3]	$ 0.19	[4]	$ 0.13	[4]	$ 0.12	[4]	$ 0.11	[4]	$ 0.67	$ 0.56		$ 0.25
Franchisor Owned Outlet [Member]
Revenue from contract with customer, excluding assessed tax	$ 104,389		$ 103,609		$ 102,741		$ 101,193		$ 100,303		$ 97,915		$ 98,355		$ 93,779		$ 411,932	$ 390,352	[2]	$ 367,310	[2]
Franchise [Member]
Revenue from contract with customer, excluding assessed tax	$ 55,160	[1]	$ 54,414	[1]	$ 54,593	[1]	$ 54,080	[1]	$ 35,196		$ 34,469		$ 35,021		$ 34,131		$ 218,247	$ 138,817		$ 139,638

[1] During 2018, we adopted ASU 2014-09, which clarifies the principles used to recognize revenue. We elected to apply the modified retrospective method of adoption; therefore, results for reporting periods after December 28, 2017 are presented under the new guidance and prior period amounts have not been adjusted. The increase in operating revenue was primarily the result of recognizing advertising revenue on a gross basis versus recording it on a net basis as previously reported. See Note 3 to our Consolidated Financial Statements for details.

[2] As disclosed in Note 2, prior period amounts have not been adjusted under the modified retrospective method of adoption of Topic 606.

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

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