Other Comprehensive Income (Loss) - Roll-Forward for AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	$ 5,172,375	$ 5,072,017
Balance, end of year	5,147,551	5,172,375	$ 5,072,017
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	(288,162)	(316,281)	(481,511)
Other comprehensive income (loss) before reclassifications	141,481	13,903	132,769
Less: Amounts reclassified from AOCI	(12,287)	(14,216)	(32,461)
Balance, end of year	(134,394)	(288,162)	(316,281)
Net unrealized gains and (losses) on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	(257,878)	(266,948)	(408,496)
Other comprehensive income (loss) before reclassifications	129,763	(2,835)	120,139
Less: Amounts reclassified from AOCI	(7,429)	(11,905)	(21,409)
Balance, end of year	(120,686)	(257,878)	(266,948)
Net benefit plan assets and (obligations) recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of year	(30,284)	(49,333)	(73,015)
Other comprehensive income (loss) before reclassifications	11,718	16,738	12,630
Less: Amounts reclassified from AOCI	(4,858)	(2,311)	(11,052)
Balance, end of year	$ (13,708)	$ (30,284)	$ (49,333)