Investment Securities - Age of Unrealized Losses and Fair Value of Related Debt Securities Held to Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Fair Value
Less than 12 Months	$ 340,866	$ 1,610,100
More than 12 Months	2,680,486	1,492,658
Total	3,021,352	3,102,758
Unrealized Losses
Less than 12 Months	(10,608)	(183,528)
More than 12 Months	(478,307)	(318,091)
Total	(488,915)	(501,619)
U.S. Treasury securities
Fair Value
Less than 12 Months	30,998	65,889
More than 12 Months	34,677	0
Total	65,675	65,889
Unrealized Losses
Less than 12 Months	(598)	(1,022)
More than 12 Months	(306)	0
Total	(904)	(1,022)
U.S. government agency securities
Fair Value
Less than 12 Months	0	209,863
More than 12 Months	213,885	1,673
Total	213,885	211,536
Unrealized Losses
Less than 12 Months	0	(47,508)
More than 12 Months	(46,158)	(172)
Total	(46,158)	(47,680)
Obligations of states and state agencies
Fair Value
Less than 12 Months	25,298	62,443
More than 12 Months	44,869	18,231
Total	70,167	80,674
Unrealized Losses
Less than 12 Months	(623)	(2,020)
More than 12 Months	(4,489)	(1,849)
Total	(5,112)	(3,869)
Municipal bonds
Fair Value
Less than 12 Months	84,224	251,970
More than 12 Months	200,924	15,534
Total	285,148	267,504
Unrealized Losses
Less than 12 Months	(1,437)	(20,457)
More than 12 Months	(19,693)	(3,158)
Total	(21,130)	(23,615)
Obligations of states and political subdivisions
Fair Value
Less than 12 Months	109,522	314,413
More than 12 Months	245,793	33,765
Total	355,315	348,178
Unrealized Losses
Less than 12 Months	(2,060)	(22,477)
More than 12 Months	(24,182)	(5,007)
Total	(26,242)	(27,484)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	182,290	962,690
More than 12 Months	2,107,464	1,413,590
Total	2,289,754	2,376,280
Unrealized Losses
Less than 12 Months	(6,756)	(109,532)
More than 12 Months	(393,858)	(305,500)
Total	(400,614)	(415,032)
Trust preferred securities
Fair Value
Less than 12 Months	0	0
More than 12 Months	28,343	30,105
Total	28,343	30,105
Unrealized Losses
Less than 12 Months	0	0
More than 12 Months	(7,709)	(5,938)
Total	(7,709)	(5,938)
Corporate and other debt securities
Fair Value
Less than 12 Months	18,056	57,245
More than 12 Months	50,324	13,525
Total	68,380	70,770
Unrealized Losses
Less than 12 Months	(1,194)	(2,989)
More than 12 Months	(6,094)	(1,474)
Total	$ (7,288)	$ (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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