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Loans Held for Investment - Student Loan Portfolio Average Balances (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Receivables [Abstract] |  |  |
Average balance of Private Education Loans | $ 9,819,053 | $ 7,563,356 | $ 5,996,651
Average Balance, FFELP Loans | 1,179,723 | 1,353,497 | 1,142,979
Average Balance, Total portfolio | $ 10,998,776 | $ 8,916,853 | $ 7,139,630
Weighted Average Interest Rate, Private Education Loans | 7.93% | 8.16% | 8.16%
Weighted Average Interest Rate, FFELP Loans | 3.26% | 3.24% | 3.32%

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- Definition Average balance of Private Education Loans + References No definition available. + Details
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