Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Less than 12 Months	$ 170,165	$ 136,920
More than 12 Months	2,698,265	2,751,924
Total	2,868,430	2,888,844
Unrealized Losses
Less than 12 Months	(1,537)	(1,368)
More than 12 Months	(496,318)	(443,384)
Total	(497,855)	(444,752)
U.S. Treasury securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	25,742	25,978
Total	25,742	25,978
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(306)	(254)
Total	(306)	(254)
U.S. government agency securities
Fair Value
Less than 12 Months	42,760	43,664
More than 12 Months	216,293	216,759
Total	259,053	260,423
Unrealized Losses
Less than 12 Months	(187)	(151)
More than 12 Months	(45,181)	(44,290)
Total	(45,368)	(44,441)
Obligations of states and state agencies
Fair Value
Less than 12 Months	7,271	10,700
More than 12 Months	57,008	48,149
Total	64,279	58,849
Unrealized Losses
Less than 12 Months	(124)	(102)
More than 12 Months	(4,508)	(4,053)
Total	(4,632)	(4,155)
Municipal bonds
Fair Value
Less than 12 Months	45,923	11,958
More than 12 Months	210,292	207,520
Total	256,215	219,478
Unrealized Losses
Less than 12 Months	(307)	(121)
More than 12 Months	(17,742)	(14,259)
Total	(18,049)	(14,380)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	53,194	22,658
More than 12 Months	267,300	255,669
Total	320,494	278,327
Unrealized Losses
Less than 12 Months	(431)	(223)
More than 12 Months	(22,250)	(18,312)
Total	(22,681)	(18,535)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	46,777	57,085
More than 12 Months	2,104,844	2,164,704
Total	2,151,621	2,221,789
Unrealized Losses
Less than 12 Months	(353)	(505)
More than 12 Months	(417,284)	(368,931)
Total	(417,637)	(369,436)
Trust preferred securities
Fair Value
Less than 12 Months	951	938
More than 12 Months	29,532	29,712
Total	30,483	30,650
Unrealized Losses
Less than 12 Months	(49)	(63)
More than 12 Months	(6,535)	(6,349)
Total	(6,584)	(6,412)
Corporate and other debt securities
Fair Value
Less than 12 Months	26,483	12,575
More than 12 Months	54,554	59,102
Total	81,037	71,677
Unrealized Losses
Less than 12 Months	(517)	(426)
More than 12 Months	(4,762)	(5,248)
Total	$ (5,279)	$ (5,674)

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

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-Topic 320
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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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