Accounts Payable and Other Accrued Liabilities - Summary of Accounts Payable and Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accounts payable	$ 28,972	$ 10,546
Sales taxes and vehicle licenses and fees	22,604	9,034
Reserve for returns and cancellations	9,501	4,545
Accrued compensation and benefits	7,991	5,054
Accrued property and equipment	7,138	8,325
Accrued advertising costs	3,835	4,265
Accrued interest	2,506	774
Other accrued liabilities	14,314	7,763
Total accounts payable and other accrued liabilities	$ 96,861	$ 50,306