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Borrowings - Securitizations (Details) - USD ($) | Jul. 31, 2016 | May 31, 2016 | Jul. 31, 2015 | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | --- | --- | --- | ---
Securities Financing Transaction [Line Items] |  |  |  |  |
Total bonds issued |  |  |  | $ 1,108,000,000 | $ 630,800,000
Total loan and accrued interest amount securitized at inception on-balance sheet term securitization |  | $ 1,364,481,000 | $ 745,580,000 |  |
2015-B |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Total bonds issued |  |  | $ 630,800,000 |  |
Weighted Average Life (in years) |  |  | 4 years 9 months 26 days |  |
2016-A |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Total bonds issued |  | $ 501,000,000 |  |  |
Weighted Average Life (in years) |  | 4 years 3 days |  |  |
2016-B |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Total bonds issued | $ 607,000,000 |  |  |  |
Weighted Average Life (in years) | 4 years 3 days |  |  |  |
LIBOR | 2015-B |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Basis spread on variable rate |  |  | 1.53% |  |
LIBOR | 2016-A |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Basis spread on variable rate |  | 1.38% |  |  |
LIBOR | 2016-B |  |  |  |  |
Securities Financing Transaction [Line Items] |  |  |  |  |
Basis spread on variable rate | 1.36% |  |  |  |

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