Investment Securities - Fair Value of Investments with Sustained Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	$ 66,643	$ 507,751
Available-for-sale, Less than 12 months, Unrealized Losses	(3,253)	(70,248)
Available-for-sale, 12 months or longer, Fair Value	1,039,657	677,083
Available-for-sale, 12 months or longer, Unrealized losses	(250,785)	(143,282)
Available-for-sale, Total Fair Value	1,106,300	1,184,834
Available-for-sale, Total Unrealized Losses	(254,038)	(213,530)
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	3,204	57,007
Available-for-sale, Less than 12 months, Unrealized Losses	(38)	(3,493)
Available-for-sale, 12 months or longer, Fair Value	208,428	163,520
Available-for-sale, 12 months or longer, Unrealized losses	(33,681)	(28,914)
Available-for-sale, Total Fair Value	211,632	220,527
Available-for-sale, Total Unrealized Losses	(33,719)	(32,407)
Obligations of States and Political Subdivisions
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	41,664	220,102
Available-for-sale, Less than 12 months, Unrealized Losses	(2,467)	(43,221)
Available-for-sale, 12 months or longer, Fair Value	219,250	45,419
Available-for-sale, 12 months or longer, Unrealized losses	(72,090)	(16,624)
Available-for-sale, Total Fair Value	260,914	265,521
Available-for-sale, Total Unrealized Losses	(74,557)	(59,845)
Mortgage-backed Securities: GSE Residential
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	16,495	165,966
Available-for-sale, Less than 12 months, Unrealized Losses	(278)	(19,859)
Available-for-sale, 12 months or longer, Fair Value	555,338	461,446
Available-for-sale, 12 months or longer, Unrealized losses	(139,349)	(96,900)
Available-for-sale, Total Fair Value	571,833	627,412
Available-for-sale, Total Unrealized Losses	(139,627)	(116,759)
Other Securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	5,280	64,676
Available-for-sale, Less than 12 months, Unrealized Losses	(470)	(3,675)
Available-for-sale, 12 months or longer, Fair Value	56,641	6,698
Available-for-sale, 12 months or longer, Unrealized losses	(5,665)	(844)
Available-for-sale, Total Fair Value	61,921	71,374
Available-for-sale, Total Unrealized Losses	$ (6,135)	$ (4,519)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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