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Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 2,428,037 | $ 2,563,984
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 3,928 | 1,306
Gross Unrealized Losses | (148,703) | (153,668)
Estimated Fair Value | 2,283,262 | 2,411,622
Mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 509,861 | 468,204
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 206 | 703
Gross Unrealized Losses | (73,956) | (62,480)
Estimated Fair Value | 436,111 | 406,427
Utah Housing Corporation bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 3,201 | 3,408
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (320) | (279)
Estimated Fair Value | 2,881 | 3,129
U.S. government-sponsored enterprises and Treasuries |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,296,942 | 1,645,609
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (55,211) | (66,870)
Estimated Fair Value | 1,241,731 | 1,578,739
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 618,033 | 446,763
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 3,722 | 603
Gross Unrealized Losses | (19,216) | (24,039)
Estimated Fair Value | $ 602,539 | $ 423,327

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