Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value
Less than Twelve Months	$ 136,920	$ 1,610,100
More than Twelve Months	2,751,924	1,492,658
Total	2,888,844	3,102,758
Unrealized Losses
Less than Twelve Months	(1,368)	(183,528)
More than Twelve Months	(443,384)	(318,091)
Total	(444,752)	(501,619)
U.S. Treasury securities
Fair Value
Less than Twelve Months	0	65,889
More than Twelve Months	25,978	0
Total	25,978	65,889
Unrealized Losses
Less than Twelve Months	0	(1,022)
More than Twelve Months	(254)	0
Total	(254)	(1,022)
U.S. government agency securities
Fair Value
Less than Twelve Months	43,664	209,863
More than Twelve Months	216,759	1,673
Total	260,423	211,536
Unrealized Losses
Less than Twelve Months	(151)	(47,508)
More than Twelve Months	(44,290)	(172)
Total	(44,441)	(47,680)
Obligations of states and state agencies
Fair Value
Less than Twelve Months	10,700	62,443
More than Twelve Months	48,149	18,231
Total	58,849	80,674
Unrealized Losses
Less than Twelve Months	(102)	(2,020)
More than Twelve Months	(4,053)	(1,849)
Total	(4,155)	(3,869)
Municipal bonds
Fair Value
Less than Twelve Months	11,958	251,970
More than Twelve Months	207,520	15,534
Total	219,478	267,504
Unrealized Losses
Less than Twelve Months	(121)	(20,457)
More than Twelve Months	(14,259)	(3,158)
Total	(14,380)	(23,615)
Total obligations of states and political subdivisions
Fair Value
Less than Twelve Months	22,658	314,413
More than Twelve Months	255,669	33,765
Total	278,327	348,178
Unrealized Losses
Less than Twelve Months	(223)	(22,477)
More than Twelve Months	(18,312)	(5,007)
Total	(18,535)	(27,484)
Residential mortgage-backed securities
Fair Value
Less than Twelve Months	57,085	962,690
More than Twelve Months	2,164,704	1,413,590
Total	2,221,789	2,376,280
Unrealized Losses
Less than Twelve Months	(505)	(109,532)
More than Twelve Months	(368,931)	(305,500)
Total	(369,436)	(415,032)
Trust preferred securities
Fair Value
Less than Twelve Months	938	0
More than Twelve Months	29,712	30,105
Total	30,650	30,105
Unrealized Losses
Less than Twelve Months	(63)	0
More than Twelve Months	(6,349)	(5,938)
Total	(6,412)	(5,938)
Corporate and other debt securities
Fair Value
Less than Twelve Months	12,575	57,245
More than Twelve Months	59,102	13,525
Total	71,677	70,770
Unrealized Losses
Less than Twelve Months	(426)	(2,989)
More than Twelve Months	(5,248)	(1,474)
Total	$ (5,674)	$ (4,463)