Other Comprehensive Income (Loss) - Accumulated Balances for Each Component of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 2,233,323	$ 2,208,628	$ 2,187,300	$ 2,136,016	$ 2,092,281	$ 2,116,877	$ 2,137,642	$ 2,209,853
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(199,324)	$ (191,461)	$ (192,324)	(209,037)	$ (216,052)	$ (155,398)	$ (104,569)	$ (10,443)
Unrealized losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(208,705)			(219,766)
Unrealized gains on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	17,350			18,956
Unrecognized losses on defined benefit pension and post-retirement benefit plans obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ (7,969)			$ (8,227)