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%

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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