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Securities - Asset-backed Securities (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015
Asset-backed securities |  |
Amortized Cost | $ 545,433 | $ 470,719
Fair Value | 531,838 | 456,066
Asset-backed securities |  |
Asset-backed securities |  |
Amortized Cost | 146,391 | 241,872
Fair Value | 138,407 | $ 231,908
FFEL |  |
Asset-backed securities |  |
Fair Value | 117,400 |
Credit Concentration Risk | Stockholders' Equity | Access Group | Asset-backed securities |  |
Asset-backed securities |  |
Amortized Cost | 37,812 |
Fair Value | 34,678 |
Credit Concentration Risk | Stockholders' Equity | Northstar Education Finance | Asset-backed securities |  |
Asset-backed securities |  |
Amortized Cost | 20,302 |
Fair Value | $ 19,792 |
Minimum | Credit Concentration Risk | Stockholders' Equity | Access Group | Asset-backed securities |  |
Asset-backed securities |  |
Credit risk as a percentage of benchmark | 10.00% |
Minimum | Credit Concentration Risk | Stockholders' Equity | Northstar Education Finance | Asset-backed securities |  |
Asset-backed securities |  |
Credit risk as a percentage of benchmark | 10.00% |

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