Other Comprehensive Income (Loss) - Roll-Forward for AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	$ 4,861,382	$ 4,698,986
Balance, end of year	4,642,740	4,861,382	$ 4,698,986
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	119,697	216,821	72,708
Other comprehensive income (loss) before reclassifications	(622,230)	(96,590)	142,448
Less: Amounts reclassified from AOCI	(21,022)	534	(1,665)
Balance, end of year	(481,511)	119,697	216,821
Net unrealized gains and losses on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	150,038	272,137	138,521
Other comprehensive income (loss) before reclassifications	(566,324)	(113,839)	144,566
Less: Amounts reclassified from AOCI	(7,790)	8,260	10,950
Balance, end of year	(408,496)	150,038	272,137
Net benefit plan assets and obligations recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	(30,341)	(55,316)	(65,813)
Other comprehensive income (loss) before reclassifications	(55,906)	17,249	(2,118)
Less: Amounts reclassified from AOCI	(13,232)	(7,726)	(12,615)
Balance, end of year	$ (73,015)	$ (30,341)	$ (55,316)