Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Net of tax
Balance	$ 2,550,312	$ 2,359,738	$ 2,486,066	$ 2,269,005
Other comprehensive income (loss)	66,474	(35,995)	77,552	(9,477)
Balance	2,648,034	2,351,009	2,648,034	2,351,009
Accumulated Other Comprehensive Income (Loss)
Net of tax
Balance	(519,132)	(612,736)	(530,210)	(639,254)
Other comprehensive income (loss)	66,474	(35,995)	77,552	(9,477)
Balance	(452,658)	(648,731)	(452,658)	(648,731)
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)	66,101	(36,985)	76,452	(10,746)
Available-for-sale Investment securities
Net of tax
Balance	(228,076)	(284,100)	(222,423)	(292,175)
Other comprehensive income (loss)	55,893	(45,369)	50,240	(37,294)
Balance	(172,183)	(329,469)	(172,183)	(329,469)
Held-to-Maturity Investment Securities
Net of tax
Balance	(285,607)	(318,782)	(301,611)	(336,946)
Other comprehensive income (loss)	10,208	8,384	26,212	26,548
Balance	(275,399)	(310,398)	(275,399)	(310,398)
Cash Flow Derivative Hedges
Net of tax
Balance	(76)	(4,423)	(803)	(4,702)
Other comprehensive income (loss)	373	990	1,100	1,269
Balance	$ 297	$ (3,433)	$ 297	$ (3,433)