Goodwill and Intangible Assets, Net - Narrative (Details) - USD ($) $ in Thousands, shares in Millions		3 Months Ended	9 Months Ended
	Apr. 12, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill		$ 9,353	$ 9,353	$ 0
Amortization expense		400	$ 700
Class A Common Units
Business Acquisition [Line Items]
Number of shares issued to former stockholders (in shares)	0.5
Car360
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired	$ 16,700
Cash acquired	400
Payments to acquire businesses, net	6,700
Number of shares issued to former stockholders (in shares)			0.5
Fair value, equity interested issued	10,000		$ 10,000
Acquired net working capital	200
Fair value, intangible assets	9,900
Deferred tax liability	2,500	2,500	2,500
Goodwill	$ 9,400	$ 9,353	$ 9,353
Weighted average amortization period, definite-lived intangible assets			6 years 3 months 18 days