Other Comprehensive Income - Rollforward of AOCI (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 5,072,017
Other comprehensive income (loss) before reclassifications	99,226
Less: Amounts reclassified from AOCI	(12,994)
Balance, end of period	5,294,076
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(316,281)
Balance, end of period	(204,061)
Net unrealized gains and (losses) on available-for-sale securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(266,948)
Other comprehensive income (loss) before reclassifications	99,226
Less: Amounts reclassified from AOCI	(11,378)
Balance, end of period	(156,344)
Net benefit plan assets and (obligations) recognized in shareholders' equity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(49,333)
Other comprehensive income (loss) before reclassifications	0
Less: Amounts reclassified from AOCI	(1,616)
Balance, end of period	$ (47,717)