Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net of tax
Balance	$ 2,513,761	$ 2,329,012	$ 2,486,066	$ 2,269,005
Other comprehensive income (loss)	4,648	(1,057)	11,078	26,518
Balance	2,550,312	2,359,738	2,550,312	2,359,738
Accumulated Other Comprehensive Income (Loss)
Net of tax
Balance	(523,780)	(611,679)	(530,210)	(639,254)
Other comprehensive income (loss)	4,648	(1,057)	11,078	26,518
Balance	(519,132)	(612,736)	(519,132)	(612,736)
Pensions and Other Benefits
Net of tax
Balance	(5,373)	(5,431)	(5,373)	(5,431)
Balance	(5,373)	(5,431)	(5,373)	(5,431)
Investment securities
Net of tax
Other comprehensive income (loss)	4,684	(705)	10,351	26,239
Available-for-sale Investment securities
Net of tax
Balance	(224,940)	(273,816)	(222,423)	(292,175)
Other comprehensive income (loss)	(3,136)	(10,284)	(5,653)	8,075
Balance	(228,076)	(284,100)	(228,076)	(284,100)
Held-to-Maturity Investment Securities
Net of tax
Balance	(293,427)	(328,361)	(301,611)	(336,946)
Other comprehensive income (loss)	7,820	9,579	16,004	18,164
Balance	(285,607)	(318,782)	(285,607)	(318,782)
Cash Flow Derivative Hedges
Net of tax
Balance	(40)	(4,071)	(803)	(4,702)
Other comprehensive income (loss)	(36)	(352)	727	279
Balance	$ (76)	$ (4,423)	$ (76)	$ (4,423)