Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 6,737,737	$ 6,575,184	$ 6,701,391	$ 6,400,802
Other comprehensive income before reclassification	48,023	(37,115)	32,218	(38,771)
Amounts reclassified from other comprehensive income	(182)	(30)	(534)	881
Other comprehensive income (loss) , net	47,841	(37,145)	31,684	(37,890)
Ending balance	6,972,380	6,627,299	6,972,380	6,627,299
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(162,613)	(164,747)	(146,456)	(164,002)
Ending balance	(114,772)	(201,892)	(114,772)	(201,892)
Unrealized Gains and Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(131,299)	(128,699)	(115,502)	(127,818)
Other comprehensive income before reclassification	48,023	(37,115)	32,218	(37,996)
Amounts reclassified from other comprehensive income	1	5	9	5
Other comprehensive income (loss) , net	48,024	(37,110)	32,227	(37,991)
Ending balance	(83,275)	(165,809)	(83,275)	(165,809)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	1,682	2,353	2,114	2,233
Other comprehensive income before reclassification	0	0	0	(775)
Amounts reclassified from other comprehensive income	(219)	(43)	(651)	852
Other comprehensive income (loss) , net	(219)	(43)	(651)	77
Ending balance	1,463	2,310	1,463	2,310
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(32,996)	(38,401)	(33,068)	(38,417)
Other comprehensive income before reclassification	0	0	0	0
Amounts reclassified from other comprehensive income	36	8	108	24
Other comprehensive income (loss) , net	36	8	108	24
Ending balance	$ (32,960)	$ (38,393)	$ (32,960)	$ (38,393)