Revenue Information and Deferred Sales Commissions Revenue Information and Deferred Sales Commissions - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue Information
Revenues (includes related party contra revenue of $1,189, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	$ 353,880	$ 353,571	$ 323,149
Dealer revenue
Revenue Information
Revenues (includes related party contra revenue of $1,189, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	317,965	304,596	280,563
OEM incentives revenue
Revenue Information
Revenues (includes related party contra revenue of $1,189, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	16,569	30,012	23,277
Forecasts, consulting and other revenue
Revenue Information
Revenues (includes related party contra revenue of $1,189, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	$ 19,346	$ 18,963	$ 19,309