Accumulated Other Comprehensive Loss - Changes, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net of tax
Balance	$ 2,252,611	$ 2,731,341	$ 2,656,912	$ 2,744,104
Unrealized net losses related to the transfer of securities from available-for-sale to held-to-maturity			(372,400)
Other comprehensive (loss) income	(87,299)	(31,761)	(537,063)	(93,067)
Balance	2,200,651	2,711,734	2,200,651	2,711,734
Accumulated Other Comprehensive Income (Loss)
Net of tax
Balance	(571,457)	(29,702)	(121,693)	31,604
Other comprehensive (loss) income	(87,299)	(31,761)	(537,063)	(93,067)
Balance	(658,756)	(61,463)	(658,756)	(61,463)
Pensions and Other Benefits
Net of tax
Balance	(24,390)	(31,737)	(24,390)	(31,737)
Balance	(24,390)	(31,737)	(24,390)	(31,737)
Available-for-sale Investment securities
Net of tax
Balance	(220,021)	2,035	(97,303)	63,341
Unrealized net losses related to the transfer of securities from available-for-sale to held-to-maturity	33,603		372,419
Other comprehensive (loss) income	(95,323)	(31,761)	(556,857)	(93,067)
Balance	(281,741)	$ (29,726)	(281,741)	$ (29,726)
Reclassification of net losses (gains) to net income, Pre-tax Amount	(15,217)		(35,146)
Held-to-Maturity Investment Securities
Net of tax
Balance	(324,204)
Unrealized net losses related to the transfer of securities from available-for-sale to held-to-maturity	(33,603)		(372,419)
Other comprehensive (loss) income	11,159		25,771
Balance	(346,648)		(346,648)
Cash Flow Derivative Hedges
Net of tax
Balance	(2,842)
Other comprehensive (loss) income	(3,135)		(5,977)
Balance	(5,977)		(5,977)
Reclassification of net losses (gains) to net income, Pre-tax Amount	$ (98)		$ 540