Summary of Significant Accounting Policies - Schedule of Account Activity Related to Resale Value Guarantee Program (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Resale Value Guarantee
Increase in resale value guarantee			$ (141,044)	$ (322,244)
Resale Value Guarantee [Member]
Operating Lease Vehicles
Operating lease vehicles— beginning of period	$ 2,835,674	$ 2,126,581	2,462,061	1,556,529
Net increase in operating lease vehicles	237,853	375,287	904,767	1,085,551
Depreciation expense recorded in cost of automotive leasing revenues	(96,995)	(71,454)	(269,012)	(179,087)
Additional depreciation expense recorded in cost of automotive leasing revenues as a result of early cancellation of resale value guarantee	(2,416)	(5,509)	(14,631)	(11,166)
Additional depreciation expense recorded in cost of automotive leasing revenues as a result of expiration	(32,489)	(55,009)	(105,378)	(55,009)
Increases to inventory from vehicles returned under our trade-in program and exercises of resale value guarantee	(14,700)	(18,718)	(50,880)	(45,640)
Operating lease vehicles—end of period	2,926,927	2,351,178	2,926,927	2,351,178
Deferred Revenue
Deferred revenue—beginning of period	1,006,600	851,684	916,652	679,132
Net increase in deferred revenue from new vehicle deliveries and reclassification of collateralized borrowing from long-term to short-term	155,133	188,113	559,996	574,226
Amortization of deferred revenue and short-term collateralized borrowing recorded in automotive leasing revenue	(171,763)	(125,411)	(474,949)	(330,093)
Additional revenue recorded in automotive leasing revenue as a result of early cancellation of resale value guarantee	(394)	(1,521)	(2,746)	(4,333)
Recognition of deferred revenue resulting from return of vehicle under trade-in program, expiration, and exercises of resale value guarantee	(3,118)	(3,456)	(12,495)	(9,523)
Deferred revenue—end of period	986,458	909,409	986,458	909,409
Resale Value Guarantee
Resale value guarantee liability—beginning of period	2,835,849	2,007,347	2,389,927	1,430,573
Increase in resale value guarantee	240,134	361,434	922,342	1,013,369
Reclassification from long-term to short-term collateralized borrowing	(74,252)	(33,129)	(189,733)	(79,171)
Additional revenue recorded in automotive leasing revenue as a result of early cancellation of resale value guarantee	(1,322)	(4,291)	(9,570)	(10,110)
Release of resale value guarantee resulting from return of vehicle under trade-in program and exercises	(14,372)	(15,516)	(54,205)	(38,816)
Release of resale value guarantee resulting from expiration of resale value guarantee	(32,481)	(55,722)	(105,205)	(55,722)
Resale value guarantee liability—end of period	$ 2,953,556	$ 2,260,123	$ 2,953,556	$ 2,260,123