Accumulated Other Comprehensive (Loss) Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 2,642,152	$ 2,471,093	$ 2,579,757	$ 2,712,680
OCI before reclassifications	(101,399)	(142,857)	(112,383)	(425,030)
Amounts reclassified from AOCI	6,435	2,467	20,630	696
Ending Balance	2,566,693	2,471,159	2,566,693	2,471,159
Unrealized Gains (Losses) on Investment Securities
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(311,816)	(249,427)	(316,231)	40,440
OCI before reclassifications	(105,050)	(120,385)	(103,628)	(362,596)
Amounts reclassified from AOCI	0	(41)	14	(20)
Ending Balance	(415,372)	(368,200)	(415,372)	(368,200)
Net Unrealized Gain (Loss) on Interest Rate Derivatives used in Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(60,029)	(46,620)	(61,776)	(4,816)
OCI before reclassifications	3,651	(22,472)	(8,755)	(62,434)
Amounts reclassified from AOCI	6,420	2,483	20,573	641
Ending Balance	(49,958)	(66,609)	(49,958)	(66,609)
Unrecognized Pension and Postretirement Plan Income (Costs)
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(7,441)	(8,163)	(7,469)	(8,213)
OCI before reclassifications	0	0	0	0
Amounts reclassified from AOCI	15	25	43	75
Ending Balance	(7,426)	(8,138)	(7,426)	(8,138)
Total
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(379,286)	(304,210)	(385,476)	27,411
Ending Balance	(472,756)	(442,947)	(472,756)	(442,947)
Reclassification out of Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	1,494	1,653	4,473	(46,024)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Investment Securities
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	1,494	1,653	4,473	(46,024)
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gain (Loss) on Interest Rate Derivatives used in Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Amounts reclassified from AOCI	0	0	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	$ 0	$ 0