Acquisitions - Purchase Consideration Allocation (Details) - USD ($) $ in Thousands	Sep. 30, 2019	May 30, 2019	Dec. 31, 2018	Aug. 10, 2018	Jan. 01, 2018
Business Acquisition [Line Items]
Goodwill	$ 206,752		$ 199,513
Maine Acquisition
Business Acquisition [Line Items]
Fixed assets		$ 999
Unfavorable leases, net		(140)
Other assets		78
Goodwill		7,239
Liabilities assumed, including deferred revenues		(145)
Net assets acquired		14,801
Colorado Acquisition
Business Acquisition [Line Items]
Fixed assets				$ 3,873
Other assets				143
Goodwill				8,476
Liabilities assumed, including deferred revenues				(83)
Net assets acquired				17,239
Long Island Acquisition
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 | Maine Acquisition
Business Acquisition [Line Items]
Intangible assets		6,740
Reacquired franchise rights | Colorado Acquisition
Business Acquisition [Line Items]
Intangible assets				4,610
Reacquired franchise rights | Long Island Acquisition
Business Acquisition [Line Items]
Intangible assets					7,640
Customer relationships | Maine Acquisition
Business Acquisition [Line Items]
Intangible assets		$ 30
Customer relationships | Colorado Acquisition
Business Acquisition [Line Items]
Intangible assets				140
Customer relationships | Long Island Acquisition
Business Acquisition [Line Items]
Intangible assets					1,150
Favorable leases, net | Colorado Acquisition
Business Acquisition [Line Items]
Intangible assets				$ 80
Favorable leases, net | Long Island Acquisition
Business Acquisition [Line Items]
Intangible assets					520
Reacquired area development rights | Long Island Acquisition
Business Acquisition [Line Items]
Intangible assets					$ 150