Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,554,332	$ 2,535,568
Allowance for credit losses	0	0
Gross Unrealized Gains	35	2,917
Gross Unrealized Losses	(212,278)	(20,529)
Available-for-sale investments	2,342,089	2,517,956
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	389,067	376,313
Allowance for credit losses	0	0
Gross Unrealized Gains	2	1,857
Gross Unrealized Losses	(68,705)	(7,073)
Available-for-sale investments	320,364	371,097
Utah Housing Corporation bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,584	6,943
Allowance for credit losses	0	0
Gross Unrealized Gains	0	18
Gross Unrealized Losses	(357)	0
Available-for-sale investments	3,227	6,961
U.S. government-sponsored enterprises and Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,804,726	1,958,943
Allowance for credit losses	0	0
Gross Unrealized Gains	0	603
Gross Unrealized Losses	(115,416)	(11,893)
Available-for-sale investments	1,689,310	1,947,653
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	356,955	193,369
Allowance for credit losses	0	0
Gross Unrealized Gains	33	439
Gross Unrealized Losses	(27,800)	(1,563)
Available-for-sale investments	$ 329,188	$ 192,245

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).

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