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Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 2,487,749 | $ 2,554,332
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 396 | 35
Gross Unrealized Losses | (177,083) | (212,278)
Estimated Fair Value | 2,311,062 | 2,342,089
Mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 387,158 | 389,067
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 62 | 2
Gross Unrealized Losses | (61,886) | (68,705)
Estimated Fair Value | 325,334 | 320,364
Utah Housing Corporation bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 3,460 | 3,584
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (294) | (357)
Estimated Fair Value | 3,166 | 3,227
U.S. government-sponsored enterprises and Treasuries |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,758,032 | 1,804,726
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | (92,548) | (115,416)
Estimated Fair Value | 1,665,484 | 1,689,310
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 339,099 | 356,955
Allowance for credit losses | 0 | 0
Gross Unrealized Gains | 334 | 33
Gross Unrealized Losses | (22,355) | (27,800)
Estimated Fair Value | $ 317,078 | $ 329,188

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
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