Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value
Less than 12 Months	$ 287,031	$ 136,920
More than 12 Months	2,637,706	2,751,924
Total	2,924,737	2,888,844
Unrealized Losses
Less than 12 Months	(2,786)	(1,368)
More than 12 Months	(510,731)	(443,384)
Total	(513,517)	(444,752)
U.S. Treasury securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	25,578	25,978
Total	25,578	25,978
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(282)	(254)
Total	(282)	(254)
U.S. government agency securities
Fair Value
Less than 12 Months	41,012	43,664
More than 12 Months	215,334	216,759
Total	256,346	260,423
Unrealized Losses
Less than 12 Months	(95)	(151)
More than 12 Months	(46,756)	(44,290)
Total	(46,851)	(44,441)
Obligations of states and state agencies
Fair Value
Less than 12 Months	23,423	10,700
More than 12 Months	55,433	48,149
Total	78,856	58,849
Unrealized Losses
Less than 12 Months	(560)	(102)
More than 12 Months	(4,743)	(4,053)
Total	(5,303)	(4,155)
Municipal bonds
Fair Value
Less than 12 Months	47,542	11,958
More than 12 Months	207,639	207,520
Total	255,181	219,478
Unrealized Losses
Less than 12 Months	(990)	(121)
More than 12 Months	(20,262)	(14,259)
Total	(21,252)	(14,380)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	70,965	22,658
More than 12 Months	263,072	255,669
Total	334,037	278,327
Unrealized Losses
Less than 12 Months	(1,550)	(223)
More than 12 Months	(25,005)	(18,312)
Total	(26,555)	(18,535)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	155,245	57,085
More than 12 Months	2,042,485	2,164,704
Total	2,197,730	2,221,789
Unrealized Losses
Less than 12 Months	(950)	(505)
More than 12 Months	(426,572)	(368,931)
Total	(427,522)	(369,436)
Trust preferred securities
Fair Value
Less than 12 Months	951	938
More than 12 Months	28,897	29,712
Total	29,848	30,650
Unrealized Losses
Less than 12 Months	(49)	(63)
More than 12 Months	(7,174)	(6,349)
Total	(7,223)	(6,412)
Corporate and other debt securities
Fair Value
Less than 12 Months	18,858	12,575
More than 12 Months	62,340	59,102
Total	81,198	71,677
Unrealized Losses
Less than 12 Months	(142)	(426)
More than 12 Months	(4,942)	(5,248)
Total	$ (5,084)	$ (5,674)

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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