Goodwill and Intangible Assets - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) Store	Jun. 30, 2017 USD ($) Store	Jun. 30, 2018 USD ($) Store	Jun. 30, 2017 USD ($) Store	Dec. 31, 2017 USD ($) Store	Mar. 31, 2018 Store	Jan. 01, 2018 Store	Mar. 31, 2017 Store	Dec. 31, 2016 Store
Goodwill And Intangible Assets [Line Items]
Impairment charges			$ 0		$ 0
Number of owned and franchised locations | Store	1,608	1,403	1,608	1,403	1,518	1,565		1,367	1,313
Amortization of intangible assets	$ 4,012,000	$ 4,710,000	$ 8,025,000	$ 9,425,000
Favorable and Unfavorable Leases
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 92,000	$ 88,000	$ 183,000	$ 181,000
Assets Acquired From Franchisee
Goodwill And Intangible Assets [Line Items]
Number of owned and franchised locations | Store							6