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Securities - Amortized Cost and Fair Value (Details) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 USD ($) item | Sep. 30, 2016 USD ($) | Dec. 31, 2016 USD ($)
Securities Available-for-Sale |  |  |
Amortized Cost | $ 533,116 |  | $ 545,433
Gross Unrealized Gains | 6,824 |  | 1,011
Gross Unrealized Losses | (6,456) |  | (14,606)
Fair Value | 533,484 |  | 531,838
Other disclosures |  |  |
Purchases | 246,971 | $ 153,252 |
Sales | $ 152,476 | $ 271,374 |
Number of originators | item | 3 |  |
U.S. Treasury |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | $ 4,001 |  |
Gross Unrealized Losses | (11) |  |
Fair Value | 3,990 |  |
U.S. government agencies |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 13,475 |  | 42,511
Gross Unrealized Gains | 15 |  |
Gross Unrealized Losses | (39) |  | (977)
Fair Value | 13,451 |  | 41,534
States and political subdivisions |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 224,648 |  | 68,718
Gross Unrealized Gains | 5,173 |  | 258
Gross Unrealized Losses | (789) |  | (273)
Fair Value | 229,032 |  | 68,703
Corporate bonds |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 10,823 |  | 10,957
Gross Unrealized Gains | 20 |  | 9
Gross Unrealized Losses | (266) |  | (336)
Fair Value | 10,577 |  | 10,630
Collateralized mortgage obligations |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 81,693 |  | 174,352
Gross Unrealized Gains | 228 |  | 374
Gross Unrealized Losses | (1,535) |  | (3,799)
Fair Value | 80,386 |  | 170,927
Asset-backed securities |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 134,542 |  | 146,391
Gross Unrealized Gains | 865 |  | 341
Gross Unrealized Losses | (3,648) |  | (8,325)
Fair Value | 131,759 |  | 138,407
FFEL |  |  |
Other disclosures |  |  |
Asset-backed securities | $ 110,600 |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education | 97.00 |  |
Percentage of total added credit enhancement in the form of overcollaterization and/or subordination of outstanding principal | 10.42 |  |
FFEL | Reimbursement requests greater than 5 % |  |  |
Other disclosures |  |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education | 85.00 |  |
Percent of insured loan | 5.00 |  |
FFEL | Reimbursement requests greater than 9 % |  |  |
Other disclosures |  |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education | 75.00 |  |
Percent of insured loan | 9.00 |  |
Collateralized loan obligations |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | $ 52,803 |  | 102,504
Gross Unrealized Gains | 505 |  | 29
Gross Unrealized Losses | (49) |  | (896)
Fair Value | 53,259 |  | $ 101,637
U.S. government agency mortgage-backed |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 11,131 |  |
Gross Unrealized Gains | 18 |  |
Gross Unrealized Losses | (119) |  |
Fair Value | 11,030 |  |
GCO Education Loan Funding Corp |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 27,555 |  |
Fair Value | $ 26,505 |  |
GCO Education Loan Funding Corp | Stockholders' Equity |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark | 10.00% |  |
Towd Point Mortgage Trust |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | $ 29,544 |  |
Fair Value | $ 29,445 |  |
Towd Point Mortgage Trust | Stockholders' Equity |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark | 10.00% |  |
Student Loan Marketing Assocation |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | $ 25,654 |  |
Fair Value | $ 25,803 |  |

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