Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 7,575,421	$ 6,737,737	$ 7,435,127	$ 6,701,391
Other comprehensive income before reclassification	21,206	48,023	56,914	32,218
Amounts reclassified to earnings	(119)	(182)	(382)	(534)
Other comprehensive income (loss), net	21,087	47,841	56,532	31,684
Ending balance	7,695,374	6,972,380	7,695,374	6,972,380
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(119,889)	(162,613)	(155,334)	(146,456)
Ending balance	(98,802)	(114,772)	(98,802)	(114,772)
Unrealized Gains and Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(98,190)	(131,299)	(133,898)	(115,502)
Other comprehensive income before reclassification	21,206	48,023	56,914	32,218
Amounts reclassified to earnings	(1)	1	(1)	9
Other comprehensive income (loss), net	21,205	48,024	56,913	32,227
Ending balance	(76,985)	(83,275)	(76,985)	(83,275)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	806	1,682	1,245	2,114
Other comprehensive income before reclassification	0	0	0	0
Amounts reclassified to earnings	(222)	(219)	(661)	(651)
Other comprehensive income (loss), net	(222)	(219)	(661)	(651)
Ending balance	584	1,463	584	1,463
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,505)	(32,996)	(22,681)	(33,068)
Other comprehensive income before reclassification	0	0	0	0
Amounts reclassified to earnings	104	36	280	108
Other comprehensive income (loss), net	104	36	280	108
Ending balance	$ (22,401)	$ (32,960)	$ (22,401)	$ (32,960)