Other Comprehensive Income - Accumulated Balances for Each Component of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 2,658,078	$ 2,354,701	$ 2,322,350	$ 2,297,383	$ 2,233,323	$ 2,208,628	$ 2,187,300	$ 2,136,016
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(129,094)	$ (154,116)	$ (156,943)	(154,256)	$ (199,324)	$ (191,461)	$ (192,324)	$ (209,037)
Unrealized losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(137,019)			(163,484)
Unrealized gains on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	15,512			17,051
Unrecognized losses on defined benefit pension and post-retirement benefit plans obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ (7,587)			$ (7,823)