Inventories and Floor Plan Payables - Floor Plan Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021	Aug. 31, 2021	Dec. 31, 2020
Floor Plan Payable
Less: outstanding letters of credit	$ (16,400)			$ (17,700)
Floor Plan Facility
Floor Plan Payable
Total commitment	1,700,000	$ 1,700,000	$ 1,380,000	1,379,750
Less: borrowings, net	(1,011,345)			(522,455)
Less: outstanding letters of credit	(11,500)			(11,700)
Less: flooring line aggregate interest reduction account	(92,108)			(133,639)
Additional borrowing capacity	596,547			723,656
Less: accounts payable for sold inventory	(28,036)			(28,980)
Less: purchase commitments	34,612			39,121
Unencumbered borrowing capacity	533,899			655,555
Line of Credit | Floor Plan Facility
Floor Plan Payable
Total commitment	70,000	$ 70,000	$ 42,000	48,000
Less: borrowings, net	(20,885)			(20,885)
Additional borrowing capacity	49,115			27,115
Letters of credit | Floor Plan Facility
Floor Plan Payable
Total commitment	30,000			15,000
Less: outstanding letters of credit	(11,500)			(11,732)
Additional letters of credit capacity	$ 18,500			$ 3,268