Revenues Financial Statement Impact of Adoption (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 26, 2018	Sep. 27, 2017		Sep. 26, 2018	Sep. 27, 2017		Dec. 28, 2017	Dec. 27, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid and other current assets	$ 10,495			$ 10,495				$ 11,788
Deferred income taxes	15,595			15,595				16,945
Other current liabilities	53,911			53,911				59,246
Other noncurrent liabilities	43,888			43,888				27,951
Deficit	(317,917)			(317,917)				(334,661)
Revenue from contract with customers, excluding assessed tax	158,023	$ 132,384	[1]	470,630	$ 393,670	[1]
Costs of franchise and license revenue	28,174	9,493		85,779	29,483
Provision for income taxes	2,810	5,429		7,217	15,103
Net income	$ 10,805	$ 9,325		$ 32,190	$ 26,447
Basic net income per share	$ 0.17	$ 0.14		$ 0.50	$ 0.38
Diluted net income per share	$ 0.16	$ 0.13		$ 0.49	$ 0.37
Total comprehensive income	$ 15,363	$ 9,548		$ 37,047	$ 24,531
Deferred income tax expense				5,044	9,936
Other current assets				1,292	834
Other accrued liabilities				(7,733)	(4,834)
Other noncurrent liabilities				(2,339)	(2,285)
Net cash flows provided by operating activities				46,259	43,525
Cumulative effect adjustment recognized upon adoption of Topic 606							$ 20,976	$ (15,446)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid and other current assets	509			509
Deferred income taxes	(5,040)			(5,040)
Other current liabilities	(360)			(360)
Other noncurrent liabilities	(18,618)			(18,618)
Deficit	14,447			14,447
Costs of franchise and license revenue	(20,007)			(60,306)
Provision for income taxes	(101)			(348)
Net income	$ (289)			$ (999)
Basic net income per share	$ 0.00			$ (0.01)
Diluted net income per share	$ 0.00			$ (0.02)
Total comprehensive income	$ (289)			$ (999)
Deferred income tax expense				(348)
Other current assets				(509)
Other accrued liabilities				621
Other noncurrent liabilities				1,235
Net cash flows provided by operating activities				0
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid and other current assets	11,004			11,004
Deferred income taxes	10,555			10,555
Other current liabilities	53,551			53,551
Other noncurrent liabilities	25,270			25,270
Deficit	(303,470)			(303,470)
Costs of franchise and license revenue	8,167			25,473
Provision for income taxes	2,709			6,869
Net income	$ 10,516			$ 31,191
Basic net income per share	$ 0.17			$ 0.49
Diluted net income per share	$ 0.16			$ 0.47
Total comprehensive income	$ 15,074			$ 36,048
Deferred income tax expense				4,696
Other current assets				783
Other accrued liabilities				(7,112)
Other noncurrent liabilities				(1,104)
Net cash flows provided by operating activities				46,259
Deferred franchise revenue [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							21,000
(Deficit) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							100
Deferred Tax Asset [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							(5,400)
Other Liabilities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							(600)
Other Current Liabilities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							500
Adjustments for New Accounting Pronouncement [Member] | (Deficit) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment recognized upon adoption of Topic 606							$ (15,600)
Franchise [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	54,414	$ 34,469		163,087	$ 103,621
Franchise [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	(20,397)			(61,653)
Franchise [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	34,017			101,434
Advertising [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	19,500			58,400
Costs of franchise and license revenue	19,500			58,400
Deferred franchise revenue [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	400			1,400
Other Franchise Services [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contract with customers, excluding assessed tax	500			1,900
Costs of franchise and license revenue	$ 500			$ 1,900

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