Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Fair Value
Less than 12 Months	$ 135,461	$ 328,108
More than 12 Months	2,426,058	2,492,592
Total	2,561,519	2,820,700
Unrealized Losses
Less than 12 Months	(1,550)	(3,761)
More than 12 Months	(448,361)	(502,282)
Total	(449,911)	(506,043)
U.S. Treasury securities
Fair Value
Less than 12 Months	25,079	25,461
More than 12 Months	0	0
Total	25,079	25,461
Unrealized Losses
Less than 12 Months	(16)	(19)
More than 12 Months	0	0
Total	(16)	(19)
U.S. government agency securities
Fair Value
Less than 12 Months	0	22,621
More than 12 Months	234,270	229,143
Total	234,270	251,764
Unrealized Losses
Less than 12 Months	0	(75)
More than 12 Months	(43,324)	(48,938)
Total	(43,324)	(49,013)
Obligations of states and state agencies
Fair Value
Less than 12 Months	5,762	20,632
More than 12 Months	41,766	42,058
Total	47,528	62,690
Unrealized Losses
Less than 12 Months	(191)	(517)
More than 12 Months	(4,266)	(4,818)
Total	(4,457)	(5,335)
Municipal bonds
Fair Value
Less than 12 Months	27,598	36,766
More than 12 Months	186,299	210,723
Total	213,897	247,489
Unrealized Losses
Less than 12 Months	(444)	(440)
More than 12 Months	(25,162)	(20,362)
Total	(25,606)	(20,802)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	33,360	57,398
More than 12 Months	228,065	252,781
Total	261,425	310,179
Unrealized Losses
Less than 12 Months	(635)	(957)
More than 12 Months	(29,428)	(25,180)
Total	(30,063)	(26,137)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	59,062	216,651
More than 12 Months	1,876,157	1,917,644
Total	1,935,219	2,134,295
Unrealized Losses
Less than 12 Months	(859)	(2,687)
More than 12 Months	(366,941)	(417,895)
Total	(367,800)	(420,582)
Trust preferred securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	29,728	29,145
Total	29,728	29,145
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(6,364)	(6,936)
Total	(6,364)	(6,936)
Corporate and other debt securities
Fair Value
Less than 12 Months	17,960	5,977
More than 12 Months	57,838	63,879
Total	75,798	69,856
Unrealized Losses
Less than 12 Months	(40)	(23)
More than 12 Months	(2,304)	(3,333)
Total	$ (2,344)	$ (3,356)

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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