Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value
Less than 12 Months	$ 397,348	$ 1,610,100
More than 12 Months	2,662,783	1,492,658
Total	3,060,131	3,102,758
Unrealized Losses
Less than 12 Months	(9,811)	(183,528)
More than 12 Months	(637,856)	(318,091)
Total	(647,667)	(501,619)
U.S. Treasury securities
Fair Value
Less than 12 Months	0	65,889
More than 12 Months	65,655	0
Total	65,655	65,889
Unrealized Losses
Less than 12 Months	0	(1,022)
More than 12 Months	(753)	0
Total	(753)	(1,022)
U.S. government agency securities
Fair Value
Less than 12 Months	44,630	209,863
More than 12 Months	198,137	1,673
Total	242,767	211,536
Unrealized Losses
Less than 12 Months	(104)	(47,508)
More than 12 Months	(62,324)	(172)
Total	(62,428)	(47,680)
Obligations of states and state agencies
Fair Value
Less than 12 Months	28,861	62,443
More than 12 Months	47,812	18,231
Total	76,673	80,674
Unrealized Losses
Less than 12 Months	(1,449)	(2,020)
More than 12 Months	(6,361)	(1,849)
Total	(7,810)	(3,869)
Municipal bonds
Fair Value
Less than 12 Months	52,881	251,970
More than 12 Months	200,811	15,534
Total	253,692	267,504
Unrealized Losses
Less than 12 Months	(1,260)	(20,457)
More than 12 Months	(38,027)	(3,158)
Total	(39,287)	(23,615)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	81,742	314,413
More than 12 Months	248,623	33,765
Total	330,365	348,178
Unrealized Losses
Less than 12 Months	(2,709)	(22,477)
More than 12 Months	(44,388)	(5,007)
Total	(47,097)	(27,484)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	258,643	962,690
More than 12 Months	2,065,357	1,413,590
Total	2,324,000	2,376,280
Unrealized Losses
Less than 12 Months	(6,081)	(109,532)
More than 12 Months	(516,961)	(305,500)
Total	(523,042)	(415,032)
Trust preferred securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	29,081	30,105
Total	29,081	30,105
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(6,976)	(5,938)
Total	(6,976)	(5,938)
Corporate and other debt securities
Fair Value
Less than 12 Months	12,333	57,245
More than 12 Months	55,930	13,525
Total	68,263	70,770
Unrealized Losses
Less than 12 Months	(917)	(2,989)
More than 12 Months	(6,454)	(1,474)
Total	$ (7,371)	$ (4,463)

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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