VIEs (Cash Flow Summary) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
VIEs, Primary Beneficiary | Trusts
Variable Interest Entity [Line Items]
Assets securitized	$ 3,887,075	$ 4,913,261	$ 10,562,806	$ 9,841,723
Net proceeds from new securitizations	2,932,117	3,794,437	6,808,647	7,757,055
Net proceeds from sale of retained bonds	1,526	99,999	55,993	117,305
Cash received for servicing fees	246,545	289,634	493,288	497,959
Net distributions from Trusts	621,708	1,078,665	1,557,381	1,671,434
Total cash received from Trusts	3,801,896	5,262,735	8,915,309	10,043,753
VIE, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Receivables securitized	512,286	0	512,286	0
Net proceeds from new securitizations	460,086	0	460,086	0
Cash received for servicing fees	5,079	9,357	11,258	19,608
Total cash received from Trusts	$ 465,165	$ 9,357	$ 471,344	$ 19,608