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Investments - Gross Unrealized Losses and Fair Value for Mortgage-Backed in Unrealized Loss Position (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Less than 12 months |  |
Gross Unrealized Losses | $ (2,797) | $ (2,752)
Estimated Fair Value | 149,164 | 142,116
12 months or more |  |
Gross Unrealized Losses | (115,288) | (150,916)
Estimated Fair Value | 1,390,575 | 2,123,439
Total |  |
Gross Unrealized Losses | (118,085) | (153,668)
Estimated Fair Value | 1,539,739 | 2,265,555
Mortgage-backed securities |  |
Less than 12 months |  |
Gross Unrealized Losses | (2,723) | (531)
Estimated Fair Value | 137,585 | 51,391
12 months or more |  |
Gross Unrealized Losses | (70,512) | (61,949)
Estimated Fair Value | 290,257 | 300,318
Total |  |
Gross Unrealized Losses | (73,235) | (62,480)
Estimated Fair Value | 427,842 | 351,709
Utah Housing Corporation bonds |  |
Less than 12 months |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
12 months or more |  |
Gross Unrealized Losses | (490) | (279)
Estimated Fair Value | 2,359 | 3,129
Total |  |
Gross Unrealized Losses | (490) | (279)
Estimated Fair Value | 2,359 | 3,129
U.S. government-sponsored enterprises and Treasuries |  |
Less than 12 months |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
12 months or more |  |
Gross Unrealized Losses | (32,265) | (66,870)
Estimated Fair Value | 915,744 | 1,578,739
Total |  |
Gross Unrealized Losses | (32,265) | (66,870)
Estimated Fair Value | 915,744 | 1,578,739
Other securities |  |
Less than 12 months |  |
Gross Unrealized Losses | (74) | (2,221)
Estimated Fair Value | 11,579 | 90,725
12 months or more |  |
Gross Unrealized Losses | (12,021) | (21,818)
Estimated Fair Value | 182,215 | 241,253
Total |  |
Gross Unrealized Losses | (12,095) | (24,039)
Estimated Fair Value | $ 193,794 | $ 331,978

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