Summary of Significant Accounting Policies - Warrant (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Nov. 19, 2018
Investment [Line Items]
Accrued expenses and other current liabilities (includes related party accrued expenses of $1,299 and $218 at December 31, 2019 and 2018, respectively)	$ 20,990	$ 8,271	$ 10,908
Other liabilities	2,336	$ 5,639	$ 9,290
Common stock warrants | DealerSync
Investment [Line Items]
Warrant agreement (shares)				2,500,000
Exercise price of warrants (in dollars per share)				$ 1.60
Other assets	1,200
Accrued expenses and other current liabilities (includes related party accrued expenses of $1,299 and $218 at December 31, 2019 and 2018, respectively)	200
Other liabilities	$ 1,000