Borrowings - Secured Financing (Details) - USD ($)					1 Months Ended
	Feb. 28, 2017	Oct. 31, 2016	Jul. 31, 2016	May 31, 2016	Nov. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total Issued						$ 1,448,000,000	$ 1,782,000,000
Total loans and accrued interest amount securitized at inception						$ 1,606,804,000	$ 2,107,042,000
Issuance 2016-A
Debt Instrument [Line Items]
Total Issued				$ 501,000,000
Weighted Average Life (in years)				4 years 5 days
Issuance 2016-B
Debt Instrument [Line Items]
Total Issued			$ 607,000,000
Weighted Average Life (in years)			4 years 5 days
Issuance 2016-C
Debt Instrument [Line Items]
Total Issued		$ 674,000,000
Weighted Average Life (in years)		4 years 2 months 36 days
Issuance 2017-A
Debt Instrument [Line Items]
Total Issued	$ 772,000,000
Weighted Average Life (in years)	4 years 2 months 36 days
Derivative basis spread on variable rate	0.93%
Issuance 2017-B
Debt Instrument [Line Items]
Total Issued					$ 676,000,000
Weighted Average Life (in years)					4 years 25 days
Derivative basis spread on variable rate					0.80%
London Interbank Offered Rate (LIBOR) | Issuance 2016-A
Debt Instrument [Line Items]
Derivative basis spread on variable rate				1.38%
London Interbank Offered Rate (LIBOR) | Issuance 2016-B
Debt Instrument [Line Items]
Derivative basis spread on variable rate			1.36%
London Interbank Offered Rate (LIBOR) | Issuance 2016-C
Debt Instrument [Line Items]
Derivative basis spread on variable rate		1.15%