Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,747,064	$ 2,042,473
Allowance for credit losses	0	0
Gross Unrealized Gains	9,855	8,838
Gross Unrealized Losses	(99,942)	(118,085)
Estimated Fair Value	1,656,977	1,933,226
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	544,422	516,358
Allowance for credit losses	0	0
Gross Unrealized Gains	621	205
Gross Unrealized Losses	(64,620)	(73,235)
Estimated Fair Value	480,423	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	(409)	(490)
Estimated Fair Value	2,250	2,359
U.S. government-sponsored enterprises and Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	648,413	948,009
Allowance for credit losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(24,058)	(32,265)
Estimated Fair Value	624,355	915,744
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	551,570	575,257
Allowance for credit losses	0	0
Gross Unrealized Gains	9,234	8,633
Gross Unrealized Losses	(10,855)	(12,095)
Estimated Fair Value	$ 549,949	$ 571,795