Acquisitions - Narrative (Details) customer in Thousands, $ in Thousands		3 Months Ended		5 Months Ended	6 Months Ended		12 Months Ended
	Jul. 27, 2017 USD ($) customer state	Jun. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2018 USD ($) franchise	Jun. 30, 2017 USD ($)	Dec. 31, 2017 franchise
Business Acquisition [Line Items]
Number of Businesses Acquired | franchise					5		4
Payments to acquire businesses and asset acquisitions					$ 14,401	$ 940
SEI
Business Acquisition [Line Items]
Purchase price	$ 140,000
Number of customers entity serves | customer	90
Number of branded stores | state	104
Number of states in which entity operates | state	11
Revenue of acquiree since acquisition date		$ 32,600		$ 58,300	67,800
Earnings or loss of acquiree since acquisition date		$ 3,900		$ 2,500	8,000
Acquisition-related costs			$ 2,000
All Acquisitions Excluding SEI Acquisition
Business Acquisition [Line Items]
Payments to acquire businesses and asset acquisitions					$ 14,400	$ 900