Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Net of tax
Balance	$ 2,486,066	$ 2,269,005
Other comprehensive income (loss)	6,430	27,575
Balance	2,513,761	2,329,012
Accumulated other comprehensive Income (loss)
Net of tax
Balance	(530,210)	(639,254)
Other comprehensive income (loss)	6,430	27,575
Balance	(523,780)	(611,679)
Pensions and Other Benefits
Net of tax
Balance	(5,373)	(5,431)
Balance	(5,373)	(5,431)
Investment securities
Net of tax
Other comprehensive income (loss)	5,667	26,944
Available-for-sale Investment securities
Net of tax
Balance	(222,423)	(292,175)
Other comprehensive income (loss)	(2,517)	18,359
Balance	(224,940)	(273,816)
Held-to-Maturity Investment Securities
Net of tax
Balance	(301,611)	(336,946)
Other comprehensive income (loss)	8,184	8,585
Balance	(293,427)	(328,361)
Cash Flow Derivative Hedges.
Net of tax
Balance	(803)	(4,702)
Other comprehensive income (loss)	763	631
Balance	$ (40)	$ (4,071)