Reclassifications Out of AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains (losses), net	$ 83	$ 748	$ (1,021)
Investment securities interest revenue	578,794	557,996	552,706
Salaries and employee benefits expense	(241,443)	(224,060)	(196,440)
Other expense	(17,386)	(15,301)	(15,092)
Deposit interest expense	(14,845)	(41,772)	(66,856)
Long-term debt interest expense	(14,912)	(14,434)	(12,921)
Merger-related and other	(13,970)	(7,018)	(6,907)
Total before tax	347,763	209,445	238,712
Income tax benefit	(77,962)	(45,356)	(52,991)
Net income	269,801	164,089	185,721
Reclassifications Out of AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(1,100)	(899)	(2,997)
Reclassifications Out of AOCI | Realized gains (losses) on AFS securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities gains (losses), net	83	748	(1,021)
Income tax benefit	46	(191)	247
Net income	129	557	(774)
Reclassifications Out of AOCI | Amortization of losses included in net income on AFS securities transferred to HTM
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities interest revenue	0	(723)	(383)
Income tax benefit	0	173	92
Net income	0	(550)	(291)
Reclassifications Out of AOCI | Reclassifications related to derivative financial instruments accounted for as cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	0	0	(235)
Deposit interest expense	0	0	(102)
Long-term debt interest expense	(608)	(359)	0
Total before tax	(608)	(359)	(337)
Income tax benefit	156	91	86
Net income	(452)	(268)	(251)
Reclassifications Out of AOCI | Reclassifications related to defined benefit pension plan activity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(1,044)	(857)	(2,257)
Income tax benefit	267	219	576
Net income	(777)	(638)	(1,681)
Reclassifications Out of AOCI | Prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits expense	(469)	(531)	(640)
Reclassifications Out of AOCI | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	(575)	(326)	(59)
Reclassifications Out of AOCI | Termination of Funded Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Merger-related and other	$ 0	$ 0	$ (1,558)