Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,042,473	$ 2,563,984
Allowance for credit losses	0	0
Gross Unrealized Gains	8,838	1,306
Gross Unrealized Losses	(118,085)	(153,668)
Available-for-sale investments	1,933,226	2,411,622
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	516,358	468,204
Allowance for credit losses	0	0
Gross Unrealized Gains	205	703
Gross Unrealized Losses	(73,235)	(62,480)
Available-for-sale investments	443,328	406,427
Utah Housing Corporation bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,849	3,408
Allowance for credit losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(490)	(279)
Available-for-sale investments	2,359	3,129
U.S. government-sponsored enterprises and Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	948,009	1,645,609
Allowance for credit losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(32,265)	(66,870)
Available-for-sale investments	915,744	1,578,739
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	575,257	446,763
Allowance for credit losses	0	0
Gross Unrealized Gains	8,633	603
Gross Unrealized Losses	(12,095)	(24,039)
Available-for-sale investments	$ 571,795	$ 423,327