Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 7,499,897	$ 6,727,139	$ 7,435,127	$ 6,701,391
Other comprehensive income before reclassification	8,496	(5,600)	35,708	(15,805)
Amounts reclassified to earnings	(133)	(165)	(263)	(352)
Other comprehensive income (loss), net	8,363	(5,765)	35,445	(16,157)
Ending balance	7,575,421	6,737,737	7,575,421	6,737,737
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(128,252)	(156,848)	(155,334)	(146,456)
Ending balance	(119,889)	(162,613)	(119,889)	(162,613)
Unrealized Gains and Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(106,686)	(125,707)	(133,898)	(115,502)
Other comprehensive income before reclassification	8,496	(5,600)	35,708	(15,805)
Amounts reclassified to earnings	0	8	0	8
Other comprehensive income (loss), net	8,496	(5,592)	35,708	(15,797)
Ending balance	(98,190)	(131,299)	(98,190)	(131,299)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	1,027	1,892	1,245	2,114
Other comprehensive income before reclassification	0	0	0	0
Amounts reclassified to earnings	(221)	(210)	(439)	(432)
Other comprehensive income (loss), net	(221)	(210)	(439)	(432)
Ending balance	806	1,682	806	1,682
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,593)	(33,033)	(22,681)	(33,068)
Other comprehensive income before reclassification	0	0	0	0
Amounts reclassified to earnings	88	37	176	72
Other comprehensive income (loss), net	88	37	176	72
Ending balance	$ (22,505)	$ (32,996)	$ (22,505)	$ (32,996)