Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 6,701,391	$ 6,400,802
Other comprehensive loss before reclassification	(10,205)	19,968
Amounts reclassified from other comprehensive (loss) income	(187)	387
Other comprehensive (loss) income, net	(10,392)	20,355
Ending balance	6,727,139	6,511,581
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(146,456)	(164,002)
Ending balance	(156,848)	(143,647)
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(115,502)	(127,818)
Other comprehensive loss before reclassification	(10,205)	17,170
Amounts reclassified from other comprehensive (loss) income	0	0
Other comprehensive (loss) income, net	(10,205)	17,170
Ending balance	(125,707)	(110,648)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	2,114	2,233
Other comprehensive loss before reclassification	0	2,798
Amounts reclassified from other comprehensive (loss) income	(222)	379
Other comprehensive (loss) income, net	(222)	3,177
Ending balance	1,892	5,410
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(33,068)	(38,417)
Other comprehensive loss before reclassification	0	0
Amounts reclassified from other comprehensive (loss) income	35	8
Other comprehensive (loss) income, net	35	8
Ending balance	$ (33,033)	$ (38,409)