Asset-Backed Financing - Assets And Liabilities Of Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Apr. 30, 2020	Dec. 31, 2019
Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount		$ 27,400
Total assets
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	$ 2,703,666		$ 1,522,330
Total assets | Term asset-backed securitizations | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	2,123,635		837,927
Total assets | Asset-backed U.S. commercial paper conduit facility | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	443,364		546,928
Total assets | Asset-backed Canadian commercial paper conduit facility | Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	136,667		137,475
Finance receivables
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	2,704,750		1,491,913
Transfers accounts for as secured borrowings, assets, allowance for loan losses, carrying amount	(156,928)		(43,797)
Finance receivables | Term asset-backed securitizations | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	2,129,372		826,047
Transfers accounts for as secured borrowings, assets, allowance for loan losses, carrying amount	(124,627)		(24,935)
Finance receivables | Asset-backed U.S. commercial paper conduit facility | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	441,402		533,587
Transfers accounts for as secured borrowings, assets, allowance for loan losses, carrying amount	(25,793)		(16,076)
Finance receivables | Asset-backed Canadian commercial paper conduit facility | Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	133,976		132,279
Transfers accounts for as secured borrowings, assets, allowance for loan losses, carrying amount	(6,508)		(2,786)
Restricted cash
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	151,965		71,498
Restricted cash | Term asset-backed securitizations | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	116,268		36,037
Restricted cash | Asset-backed U.S. commercial paper conduit facility | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	26,624		27,775
Restricted cash | Asset-backed Canadian commercial paper conduit facility | Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	9,073		7,686
Other assets
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	3,879		2,716
Other assets | Term asset-backed securitizations | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	2,622		778
Other assets | Asset-backed U.S. commercial paper conduit facility | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	1,131		1,642
Other assets | Asset-backed Canadian commercial paper conduit facility | Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, assets, carrying amount	126		296
Asset-backed debt
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, liabilities, carrying amount	2,310,839		1,369,512
Asset-backed debt | Term asset-backed securitizations | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, liabilities, carrying amount	1,791,956		764,392
Asset-backed debt | Asset-backed U.S. commercial paper conduit facility | Consolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, liabilities, carrying amount	402,205		490,427
Asset-backed debt | Asset-backed Canadian commercial paper conduit facility | Unconsolidated VIEs:
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers accounts for as secured borrowings, liabilities, carrying amount	$ 116,678		$ 114,693