Accumulated Other Comprehensive (Loss) Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 3,490,447	$ 3,197,325
OCI before reclassifications	(27,637)	11,533
Amounts reclassified from AOCI	3,195	3,411
Ending Balance	3,505,283	3,274,321
Unrealized Gains (Losses) on Investment Securities
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(205,701)	(275,989)
OCI before reclassifications	(21,683)	9,769
Amounts reclassified from AOCI	0	2
Ending Balance	(226,147)	(264,890)
Net Unrealized Gains (Losses) on Interest Rate Derivatives used in Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	395	(16,052)
OCI before reclassifications	(5,954)	1,764
Amounts reclassified from AOCI	3,300	3,515
Ending Balance	(2,259)	(10,773)
Unrecognized Pension and Postretirement Plan Income (Costs)
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	6,624	4,222
OCI before reclassifications	0	0
Amounts reclassified from AOCI	(105)	(106)
Ending Balance	6,519	4,116
Total
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(198,682)	(287,819)
Ending Balance	(221,887)	(271,547)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	1,237	1,328
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Investment Securities
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	1,237	1,328
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Interest Rate Derivatives used in Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	0	0
Reclassification out of Accumulated Other Comprehensive Income | Unrecognized Pension and Postretirement Plan Income (Costs)
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	$ 0	$ 0