Borrowings - Securitizations (Details) - USD ($)	1 Months Ended
	Aug. 31, 2020	Feb. 29, 2020	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Dec. 31, 2019
Securities Financing Transaction [Line Items]
Total Issued					$ 1,343,000,000	$ 1,110,000,000
Total loan and accrued interest amount securitized at inception on-balance sheet term securitization					$ 1,463,230,000	$ 1,208,963,000
2019-A
Securities Financing Transaction [Line Items]
Total Issued				$ 453,000,000
Basis spread on variable rate				0.92%
Weighted Average Life				4 years 3 months 3 days
2019-B
Securities Financing Transaction [Line Items]
Total Issued			$ 657,000,000
Basis spread on variable rate			1.01%
Weighted Average Life			4 years 4 months 28 days
2020-A
Securities Financing Transaction [Line Items]
Total Issued		$ 636,000,000
Basis spread on variable rate		0.88%
Weighted Average Life		4 years 2 months 4 days
2020-B
Securities Financing Transaction [Line Items]
Total Issued	$ 707,000,000
Basis spread on variable rate	1.30%
Weighted Average Life	4 years 1 month 20 days