Fair Value Measurements And Disclosures - Financial Instruments Not Required to be Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Financial assets:
Cash and cash equivalents, carrying amount	$ 92,779	$ 119,774	$ 90,000
Finance receivables, net, carrying amount	3,332,748	3,514,165	$ 3,238,813	$ 3,230,949	$ 3,084,777
Financial liabilities:
Interest-bearing deposits, carrying value	119,834	106,246
Carrying Amount
Financial assets:
Cash and cash equivalents, carrying amount	92,779	119,774
Finance receivables, net, carrying amount	3,332,748	3,514,165
Financial liabilities:
Interest-bearing deposits, carrying value	119,834	106,246
Outstanding borrowings under credit facility	1,440,751	1,789,502
Term loans, carrying amount	472,500	425,000
Senior Notes, carrying amount	300,000
Convertible debt	322,438	601,086
Estimated Fair Value
Financial assets:
Cash and cash equivalents, estimated fair value	92,779	119,774
Finance receivables, net, estimated fair value	3,408,353	3,645,610
Financial liabilities:
Interest-bearing deposits, fair value	119,834	106,246
Revolving lines of credit, estimated fair value	1,440,751	1,789,502
Term loans, estimated fair value	472,500	425,000
Debt Instrument, Fair Value Disclosure	313,104
Convertible debt, estimated fair value	$ 378,720	$ 648,968