Other Comprehensive Income - Accumulated Balances for Each Component of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ 3,825,778	$ 3,778,854	$ 2,727,105	$ 2,678,318	$ 2,658,078	$ 2,354,701	$ 2,322,350	$ 2,297,383
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(101,170)	$ (114,041)	$ (121,621)	(142,608)	$ (129,094)	$ (154,116)	$ (156,943)	$ (154,256)
Unrealized losses on securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	(108,006)			(152,934)
Unrealized gains on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	13,716			17,429
Unrecognized losses on defined benefit pension and post-retirement benefit plans obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total accumulated other comprehensive loss	$ (6,880)			$ (7,103)