Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized Cost
Due in One Year or Less	$ 598,183
Due after One Year through Five Years	274,534
Due after Five Years through Ten Years	266,647
Due after Ten Years	48,689
Amortized  Cost	1,188,053	$ 1,176,040
Fair Value
Due in One Year or Less	597,983
Due after One Year through Five Years	272,619
Due after Five Years through Ten Years	235,314
Due after Ten Years	48,105
Total	1,154,021	1,140,071
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	28,341
Due after Five Years through Ten Years	41,544
Due after Ten Years	1,650,711
Total	1,720,596	1,729,667
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	26,684
Due after Five Years through Ten Years	37,681
Due after Ten Years	1,383,332
Total	1,447,697	1,485,506
Amortized Cost
Due in One Year or Less	598,183
Due after One Year through Five Years	302,875
Due after Five Years through Ten Years	308,191
Due after Ten Years	1,699,400
Total	2,908,649
Fair Value
Due in One Year or Less	597,983
Due after One Year through Five Years	299,303
Due after Five Years through Ten Years	272,995
Due after Ten Years	1,431,437
Total	2,601,718
U.S. Treasury
Amortized Cost
Due in One Year or Less	565,128
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	0
Amortized  Cost	565,128	538,899
Fair Value
Due in One Year or Less	564,939
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	0
Total	564,939	539,256
Agency
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	257
Due after Five Years through Ten Years	786
Due after Ten Years	691
Amortized  Cost	1,734	1,941
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	250
Due after Five Years through Ten Years	758
Due after Ten Years	662
Total	1,670	1,868
Corporate
Amortized Cost
Due in One Year or Less	33,006
Due after One Year through Five Years	233,484
Due after Five Years through Ten Years	204,936
Due after Ten Years	0
Amortized  Cost	471,426	481,499
Fair Value
Due in One Year or Less	32,995
Due after One Year through Five Years	231,709
Due after Five Years through Ten Years	174,178
Due after Ten Years	0
Total	438,882	446,343
Collateralized mortgage obligations
Amortized Cost
Due in One Year or Less	49
Due after One Year through Five Years	40,793
Due after Five Years through Ten Years	60,925
Due after Ten Years	47,998
Amortized  Cost	149,765	153,701
Fair Value
Due in One Year or Less	49
Due after One Year through Five Years	40,660
Due after Five Years through Ten Years	60,378
Due after Ten Years	47,443
Total	148,530	152,604
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	86
Due after Five Years through Ten Years	0
Due after Ten Years	329,751
Total	329,837	334,997
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	86
Due after Five Years through Ten Years	0
Due after Ten Years	320,172
Total	320,258	326,992
Mortgage-backed securities
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	1,918
Due after Five Years through Ten Years	3,476
Due after Ten Years	223,217
Total	228,611	232,157
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	1,977
Due after Five Years through Ten Years	3,527
Due after Ten Years	187,831
Total	193,335	201,669
Municipal bonds
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	26,337
Due after Five Years through Ten Years	38,068
Due after Ten Years	1,081,497
Total	1,145,902	1,146,244
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	24,621
Due after Five Years through Ten Years	34,154
Due after Ten Years	859,083
Total	917,858	$ 940,576
Other
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	16,246
Total	16,246
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	16,246
Total	$ 16,246