Acquisition - Purchase Consideration Allocation (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 191,038	$ 176,981	$ 176,981
Assets Acquired From Franchisee
Business Acquisition [Line Items]
Fixed assets		4,672
Other assets		275
Goodwill		14,056
Liabilities assumed, including deferred revenues		(310)
Net assets acquired		28,153
Reacquired franchise rights | Assets Acquired From Franchisee
Business Acquisition [Line Items]
Intangible assets		7,640
Customer relationships | Assets Acquired From Franchisee
Business Acquisition [Line Items]
Intangible assets		1,150
Favorable leases, net | Assets Acquired From Franchisee
Business Acquisition [Line Items]
Intangible assets		520
Reacquired area development rights | Assets Acquired From Franchisee
Business Acquisition [Line Items]
Intangible assets		$ 150