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Investments - Additional Information (Details) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 USD ($) security numberOfInvestments | Dec. 31, 2019 USD ($) security
Investment Holdings [Line Items] |  |
Vertical risk retention interest | 5.00% |
Trading investments | $ 11,360 | $ 0
Available-for-sale investments, cost | $ 607,867 | 485,756
Number of securities in net loss position | numberOfInvestments | 10 |
Par value of mortgage-backed securities pledged to FRB | $ 285,000 | 252,000
Gain on equity securities investment | 8,000 |
Non-marketable securities investment | 26,000 | 26,000
Low income housing tax credit investments | 57,000 | 58,000
Low income housing tax credit investments, liability for unfunded commitments | 25,000 | 29,000
Low income housing tax credit investments, tax credits and benefits | $ 1,000 | $ 6,000
Low income housing tax credit investments, expected tax benefits recognized | 25.00% |
Student Loan |  |
Investment Holdings [Line Items] |  |
Private education loans sold | $ 1,700,000 |
Mortgage-backed securities |  |
Investment Holdings [Line Items] |  |
Number of securities in net loss position | security | 0 | 33
Number of mortgage-backed securities | security |  | 107
Utah Housing Corporation bonds |  |
Investment Holdings [Line Items] |  |
Number of securities in net loss position | security | 1 |
Number of mortgage-backed securities | security | 3 |
U.S. government-sponsored enterprises |  |
Investment Holdings [Line Items] |  |
Number of securities in net loss position | security | 1 |
Number of government sponsored securities | security | 20 |
Ginnie Mae | Mortgage-backed securities |  |
Investment Holdings [Line Items] |  |
Available-for-sale investments, cost | $ 51,000 |
Number of securities in net loss position | security |  | 18
Number of mortgage-backed securities | security |  | 33
Fannie Mae | Mortgage-backed securities |  |
Investment Holdings [Line Items] |  |
Available-for-sale investments, cost | 104,000 |
Freddie Mac | Mortgage-backed securities |  |
Investment Holdings [Line Items] |  |
Available-for-sale investments, cost | $ 52,000 |

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