Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 6,727,139	$ 6,511,581	$ 6,701,391	$ 6,400,802
Other comprehensive loss before reclassification	(5,600)	(21,624)	(15,805)	(1,656)
Amounts reclassified from other comprehensive loss	(165)	524	(352)	911
Other comprehensive (loss) income, net	(5,765)	(21,100)	(16,157)	(745)
Ending balance	6,737,737	6,575,184	6,737,737	6,575,184
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(156,848)	(143,647)	(146,456)	(164,002)
Ending balance	(162,613)	(164,747)	(162,613)	(164,747)
Unrealized Gains and Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(125,707)	(110,648)	(115,502)	(127,818)
Other comprehensive loss before reclassification	(5,600)	(18,051)	(15,805)	(881)
Amounts reclassified from other comprehensive loss	8	0	8	0
Other comprehensive (loss) income, net	(5,592)	(18,051)	(15,797)	(881)
Ending balance	(131,299)	(128,699)	(131,299)	(128,699)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	1,892	5,410	2,114	2,233
Other comprehensive loss before reclassification	0	(3,573)	0	(775)
Amounts reclassified from other comprehensive loss	(210)	516	(432)	895
Other comprehensive (loss) income, net	(210)	(3,057)	(432)	120
Ending balance	1,682	2,353	1,682	2,353
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(33,033)	(38,409)	(33,068)	(38,417)
Other comprehensive loss before reclassification	0	0	0	0
Amounts reclassified from other comprehensive loss	37	8	72	16
Other comprehensive (loss) income, net	37	8	72	16
Ending balance	$ (32,996)	$ (38,401)	$ (32,996)	$ (38,401)