Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 6,575,184	$ 6,204,913	$ 6,400,802	$ 5,084,066
Other comprehensive loss before reclassification	(37,115)		(38,771)
Amounts reclassified from other comprehensive loss	(30)		881
Other comprehensive (loss) income, net	(37,145)	(57,220)	(37,890)	(147,625)
Ending balance	6,627,299	6,273,829	6,627,299	6,273,829
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(164,747)	(108,337)	(164,002)	(17,932)
Ending balance	(201,892)	$ (165,557)	(201,892)	$ (165,557)
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(128,699)		(127,818)
Other comprehensive loss before reclassification	(37,115)		(37,996)
Amounts reclassified from other comprehensive loss	5		5
Other comprehensive (loss) income, net	(37,110)		(37,991)
Ending balance	(165,809)		(165,809)
Unrealized Gains and Losses on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	2,353		2,233
Other comprehensive loss before reclassification	0		(775)
Amounts reclassified from other comprehensive loss	(43)		852
Other comprehensive (loss) income, net	(43)		77
Ending balance	2,310		2,310
Defined Benefit Pension and Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(38,401)		(38,417)
Other comprehensive loss before reclassification	0		0
Amounts reclassified from other comprehensive loss	8		24
Other comprehensive (loss) income, net	8		24
Ending balance	$ (38,393)		$ (38,393)