Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 238,912	$ 77,407
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(3,078)	(753)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,201,072	2,303,038
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(236,414)	(222,629)
Fair Value of Available-for-Sale Securities, Total	2,439,984	2,380,445
Unrealized Losses of Available-for-Sale Securities, Total	(239,492)	(223,382)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	81,334	35,900
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,054)	(231)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,043,695	1,090,389
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(110,772)	(98,450)
Fair Value of Held-to-Maturity Securities, Total	1,125,029	1,126,289
Unrealized Losses of Held-to-Maturity Securities	(111,826)	(98,681)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	2,705	7,152
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(16)	(32)
Fair Value of Available-for-Sale Securities, 12 Months or More	149,486	165,091
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(7,373)	(7,075)
Fair Value of Available-for-Sale Securities, Total	152,191	172,243
Unrealized Losses of Available-for-Sale Securities, Total	(7,389)	(7,107)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	14,899	0
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(101)	0
Fair Value of Held-to-Maturity Securities, 12 Months or More	27,255	42,451
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(1,657)	(1,391)
Fair Value of Held-to-Maturity Securities, Total	42,154	42,451
Unrealized Losses of Held-to-Maturity Securities	(1,758)	(1,391)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	61,250	26,462
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(559)	(136)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,053,060	1,087,888
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(143,260)	(133,863)
Fair Value of Available-for-Sale Securities, Total	1,114,310	1,114,350
Unrealized Losses of Available-for-Sale Securities, Total	(143,819)	(133,999)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	37,878	16,763
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(455)	(88)
Fair Value of Held-to-Maturity Securities, 12 Months or More	52,853	64,000
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(3,689)	(3,170)
Fair Value of Held-to-Maturity Securities, Total	90,731	80,763
Unrealized Losses of Held-to-Maturity Securities	(4,144)	(3,258)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	9,721	0
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(18)	0
Fair Value of Available-for-Sale Securities, 12 Months or More	132,805	135,255
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(8,092)	(6,984)
Fair Value of Available-for-Sale Securities, Total	142,526	135,255
Unrealized Losses of Available-for-Sale Securities, Total	(8,110)	(6,984)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	36,217	22,987
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(45)	(13)
Fair Value of Available-for-Sale Securities, 12 Months or More	41,919	44,666
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(1,092)	(914)
Fair Value of Available-for-Sale Securities, Total	78,136	67,653
Unrealized Losses of Available-for-Sale Securities, Total	(1,137)	(927)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	87,822	15,301
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,005)	(505)
Fair Value of Available-for-Sale Securities, 12 Months or More	697,559	744,922
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(68,734)	(64,898)
Fair Value of Available-for-Sale Securities, Total	785,381	760,223
Unrealized Losses of Available-for-Sale Securities, Total	(70,739)	(65,403)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	28,557	19,137
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(498)	(143)
Fair Value of Held-to-Maturity Securities, 12 Months or More	963,587	983,938
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(105,426)	(93,889)
Fair Value of Held-to-Maturity Securities, Total	992,144	1,003,075
Unrealized Losses of Held-to-Maturity Securities	(105,924)	(94,032)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	41,197	5,505
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(435)	(67)
Fair Value of Available-for-Sale Securities, 12 Months or More	126,243	125,216
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(7,863)	(8,895)
Fair Value of Available-for-Sale Securities, Total	167,440	130,721
Unrealized Losses of Available-for-Sale Securities, Total	$ (8,298)	$ (8,962)

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