Acquisitions - Narrative (Details) $ in Thousands		9 Months Ended
	Jul. 27, 2017 USD ($) customer state	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Purchase price		$ 142,278	$ 9,671
SEI
Business Acquisition [Line Items]
Purchase price	$ 140,000
Business combination, number of customers entity serves | customer	90,000
Business combination, number of branded stores | state	104
Business combination, number of states in which entity operates | state	11
Business acquisition, goodwill, expected to be deductible for tax purposes	$ 88,338
Acquired finite-lived intangible assets, weighted average useful life	3 years 3 months 18 days
Business combination, acquisition-related costs		2,000
All Acquisitions Excluding SEI Acquisition
Business Acquisition [Line Items]
Purchase price		$ 2,400	$ 9,700