Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Fair Value
Less than 12 Months	$ 145,448	$ 328,108
More than 12 Months	2,479,243	2,492,592
Total	2,624,691	2,820,700
Unrealized Losses
Less than 12 Months	(1,489)	(3,761)
More than 12 Months	(451,895)	(502,282)
Total	(453,384)	(506,043)
U.S. Treasury securities
Fair Value
Less than 12 Months	25,269	25,461
More than 12 Months	0	0
Total	25,269	25,461
Unrealized Losses
Less than 12 Months	(21)	(19)
More than 12 Months	0	0
Total	(21)	(19)
U.S. government agency securities
Fair Value
Less than 12 Months	22,109	22,621
More than 12 Months	237,231	229,143
Total	259,340	251,764
Unrealized Losses
Less than 12 Months	(58)	(75)
More than 12 Months	(40,935)	(48,938)
Total	(40,993)	(49,013)
Obligations of states and state agencies
Fair Value
Less than 12 Months	5,948	20,632
More than 12 Months	43,721	42,058
Total	49,669	62,690
Unrealized Losses
Less than 12 Months	(8)	(517)
More than 12 Months	(4,791)	(4,818)
Total	(4,799)	(5,335)
Municipal bonds
Fair Value
Less than 12 Months	35,687	36,766
More than 12 Months	191,086	210,723
Total	226,773	247,489
Unrealized Losses
Less than 12 Months	(572)	(440)
More than 12 Months	(23,758)	(20,362)
Total	(24,330)	(20,802)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	41,635	57,398
More than 12 Months	234,807	252,781
Total	276,442	310,179
Unrealized Losses
Less than 12 Months	(580)	(957)
More than 12 Months	(28,549)	(25,180)
Total	(29,129)	(26,137)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	43,444	216,651
More than 12 Months	1,920,109	1,917,644
Total	1,963,553	2,134,295
Unrealized Losses
Less than 12 Months	(821)	(2,687)
More than 12 Months	(373,243)	(417,895)
Total	(374,064)	(420,582)
Trust preferred securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	29,480	29,145
Total	29,480	29,145
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(6,606)	(6,936)
Total	(6,606)	(6,936)
Corporate and other debt securities
Fair Value
Less than 12 Months	12,991	5,977
More than 12 Months	57,616	63,879
Total	70,607	69,856
Unrealized Losses
Less than 12 Months	(9)	(23)
More than 12 Months	(2,562)	(3,333)
Total	$ (2,571)	$ (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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