Other Comprehensive Income - Rollforward of AOCI (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2025 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 5,172,375
Other comprehensive income (loss) before reclassifications	71,968
Less: Amounts reclassified from AOCI	(11,225)
Balance, end of period	5,154,944
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(288,162)
Balance, end of period	(204,969)
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	71,968
Less: Amounts reclassified from AOCI	(8,226)
Balance, end of period	(177,684)
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	(2,999)
Balance, end of period	$ (27,285)