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Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,742,863	$ 2,042,473
Allowance for credit losses	0	0
Gross Unrealized Gains	4,470	8,838
Gross Unrealized Losses	(96,677)	(118,085)
Estimated Fair Value	1,650,656	1,933,226
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	561,587	516,358
Allowance for credit losses	0	0
Gross Unrealized Gains	625	205
Gross Unrealized Losses	(63,905)	(73,235)
Estimated Fair Value	498,307	443,328
Utah Housing Corporation bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,659	2,849
Allowance for credit losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(420)	(490)
Estimated Fair Value	2,239	2,359
U.S. government-sponsored enterprises and Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	648,636	948,009
Allowance for credit losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(19,513)	(32,265)
Estimated Fair Value	629,123	915,744
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	529,981	575,257
Allowance for credit losses	0	0
Gross Unrealized Gains	3,845	8,633
Gross Unrealized Losses	(12,839)	(12,095)
Estimated Fair Value	$ 520,987	$ 571,795

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