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Securities - Amortized Cost and Fair Value (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Securities Available-for-Sale |  |  |
Amortized Cost | $ 471,961 | $ 475,146 |
Gross Unrealized Gains | 26,735 | 13,285 |
Gross Unrealized Losses | (2,518) | (3,783) |
Fair Value | 496,178 | 484,648 |
Accrued interest receivable | 2,700 | 3,200 |
Other disclosures |  |  |
Purchases | 65,229 | 159,544 | $ 75,044
Sales | 18,006 | 191,298 | 94,663
Securities pledged to secure deposits and for other purposes | 335,800 | $ 320,800 | $ 320,800
Reimbursement requests greater than 5 % |  |  |
Other disclosures |  |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education |  | 85 |
Percent of insured loan |  | 5 |
Reimbursement requests greater than 9 % |  |  |
Other disclosures |  |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education |  | 75 |
Percent of insured loan |  | 9 |
US Treasury Securities [Member] |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 4,014 | $ 4,010 |
Gross Unrealized Gains | 103 | 26 |
Fair Value | 4,117 | 4,036 |
US Treasury and Government |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 6,811 |  |
Gross Unrealized Losses | (154) |  |
Fair Value | 6,657 |  |
US Government Corporations and Agencies Securities [Member] |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost |  | 8,502 |
Gross Unrealized Losses |  | (165) |
Fair Value |  | 8,337 |
U.S. government agencies mortgage-backed |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 16,098 | 16,164 |
Gross Unrealized Gains | 1,112 | 443 |
Gross Unrealized Losses | (1) | (19) |
Fair Value | 17,209 | 16,588 |
US States and Political Subdivisions Debt Securities [Member] |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 229,352 | 240,399 |
Gross Unrealized Gains | 21,269 | 11,207 |
Gross Unrealized Losses | (1,362) | (2,431) |
Fair Value | 249,259 | 249,175 |
Collateralized Mortgage Obligations [Member] |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 53,999 | 57,059 |
Gross Unrealized Gains | 2,866 | 963 |
Gross Unrealized Losses | (280) | (38) |
Fair Value | 56,585 | 57,984 |
Asset-backed Securities [Member] |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 130,959 | 82,114 |
Gross Unrealized Gains | 1,370 | 617 |
Gross Unrealized Losses | (511) | (887) |
Fair Value | 131,818 | 81,844 |
FFEL |  |  |
Securities Available-for-Sale |  |  |
Fair Value | 105,000 | $ 105,000 |
Other disclosures |  |  |
Percentage of outstanding principal amount of loans guaranteed by US Department of Education |  | 97 |
Collateralized loan obligations |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 30,728 | $ 66,898 |
Gross Unrealized Gains | 15 | 29 |
Gross Unrealized Losses | (210) | (243) |
Fair Value | 30,533 | $ 66,684 |
GCO Education Loan Funding Corp [Member] | Stockholders' Equity, Total [Member] |  |  |
Other disclosures |  |  |
Credit risk as a percentage of benchmark |  | 1.00% |
Towd Point Mortgage Trust |  |  |
Securities Available-for-Sale |  |  |
Amortized Cost | 33,198 |  |
Fair Value | $ 35,479 |  |

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