Acquisitions - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended		12 Months Ended
	Jul. 27, 2017 USD ($) customer state	Jul. 31, 2018 USD ($) state	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) franchise	Sep. 30, 2017 USD ($)	Dec. 31, 2017 franchise
Business Acquisition [Line Items]
Additional number of businesses acquired | franchise						5		3
Payments to acquire businesses and asset acquisitions						$ 141,079	$ 142,278
Franchisee Acquisitions
Business Acquisition [Line Items]
Purchase price		$ 127,498
Number of branded stores | state		90
Consideration Transferred		$ 127,053
Revenue of acquiree since acquisition date			$ 22,500
Earnings or loss of acquiree since acquisition date			(200)
Acquisition-related costs			500
SEI
Business Acquisition [Line Items]
Purchase price	$ 140,000
Number of customers entity serves | customer	90,000
Number of branded stores | state	104
Consideration Transferred	$ 143,540
Number of states in which entity operates | state	11
Revenue of acquiree since acquisition date			31,100		$ 58,300	98,900
Earnings or loss of acquiree since acquisition date			$ 1,500		$ 2,500	9,500
Acquisition-related costs				$ 2,100
All Acquisitions Excluding SEI Acquisition
Business Acquisition [Line Items]
Payments to acquire businesses and asset acquisitions						$ 14,100	$ 2,400