Other Comprehensive Income - Rollforward of AOCI (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	$ 5,072,017
Other comprehensive income (loss) before reclassifications	(18,271)
Less: Amounts reclassified from AOCI	(8,418)
Balance, end of period	5,102,343
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(316,281)
Balance, end of period	(326,134)
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	(18,271)
Less: Amounts reclassified from AOCI	(7,879)
Balance, end of period	(277,340)
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	(539)
Balance, end of period	$ (48,794)