Other Comprehensive Income - Rollforward of AOCI (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2025 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 5,172,375
Other comprehensive income (loss) before reclassifications	46,946
Less: Amounts reclassified from AOCI	(4,771)
Balance, end of period	5,139,884
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(288,162)
Balance, end of period	(236,445)
Net unrealized gains and (losses) on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(257,878)
Other comprehensive income (loss) before reclassifications	46,946
Less: Amounts reclassified from AOCI	(4,725)
Balance, end of period	(206,207)
Net benefit plan assets and (obligations) recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(30,284)
Other comprehensive income (loss) before reclassifications	0
Less: Amounts reclassified from AOCI	(46)
Balance, end of period	$ (30,238)