Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 51,060	$ 143,467
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(1,738)	(2,794)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,712,008	2,887,122
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(260,071)	(333,485)
Fair Value of Available-for-Sale Securities, Total	2,763,068	3,030,589
Unrealized Losses of Available-for-Sale Securities, Total	(261,809)	(336,279)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	22,950	69,991
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(483)	(1,158)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,108,380	1,062,828
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(83,103)	(110,905)
Fair Value of Held-to-Maturity Securities, Total	1,131,330	1,132,819
Unrealized Losses of Held-to-Maturity Securities	(83,586)	(112,063)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	18,911	2,742
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(132)	(2)
Fair Value of Available-for-Sale Securities, 12 Months or More	171,503	180,569
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(11,116)	(17,091)
Fair Value of Available-for-Sale Securities, Total	190,414	183,311
Unrealized Losses of Available-for-Sale Securities, Total	(11,248)	(17,093)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	0	0
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	0	0
Fair Value of Held-to-Maturity Securities, 12 Months or More	41,779	40,677
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(1,712)	(2,607)
Fair Value of Held-to-Maturity Securities, Total	41,779	40,677
Unrealized Losses of Held-to-Maturity Securities	(1,712)	(2,607)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	2,314	102,831
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(23)	(2,166)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,322,911	1,392,318
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(150,047)	(189,391)
Fair Value of Available-for-Sale Securities, Total	1,325,225	1,495,149
Unrealized Losses of Available-for-Sale Securities, Total	(150,070)	(191,557)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	0	48,498
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	0	(861)
Fair Value of Held-to-Maturity Securities, 12 Months or More	72,591	65,573
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(2,288)	(3,501)
Fair Value of Held-to-Maturity Securities, Total	72,591	114,071
Unrealized Losses of Held-to-Maturity Securities	(2,288)	(4,362)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	0	9,298
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	0	(226)
Fair Value of Available-for-Sale Securities, 12 Months or More	168,230	166,107
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(9,090)	(15,891)
Fair Value of Available-for-Sale Securities, Total	168,230	175,405
Unrealized Losses of Available-for-Sale Securities, Total	(9,090)	(16,117)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	0	0
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	0	0
Fair Value of Available-for-Sale Securities, 12 Months or More	106,450	213,838
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(2,945)	(7,551)
Fair Value of Available-for-Sale Securities, Total	106,450	213,838
Unrealized Losses of Available-for-Sale Securities, Total	(2,945)	(7,551)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	22,859	28,596
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(504)	(400)
Fair Value of Available-for-Sale Securities, 12 Months or More	771,340	769,860
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(66,300)	(75,531)
Fair Value of Available-for-Sale Securities, Total	794,199	798,456
Unrealized Losses of Available-for-Sale Securities, Total	(66,804)	(75,931)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	22,950	21,493
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(483)	(297)
Fair Value of Held-to-Maturity Securities, 12 Months or More	994,010	956,578
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(79,103)	(104,797)
Fair Value of Held-to-Maturity Securities, Total	1,016,960	978,071
Unrealized Losses of Held-to-Maturity Securities	(79,586)	(105,094)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	6,976	0
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(1,079)	0
Fair Value of Available-for-Sale Securities, 12 Months or More	171,574	164,430
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(20,573)	(28,030)
Fair Value of Available-for-Sale Securities, Total	178,550	164,430
Unrealized Losses of Available-for-Sale Securities, Total	$ (21,652)	$ (28,030)

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