Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in One Year or Less	$ 99,174
Due after One Year through Five Years	592,718
Due after Five Years through Ten Years	1,050,636
Due after Ten Years	468,726
Amortized  Cost	2,211,254	$ 2,904,745
Fair Value
Due in One Year or Less	97,073
Due after One Year through Five Years	564,084
Due after Five Years through Ten Years	878,651
Due after Ten Years	374,791
Total	1,914,599	2,601,013
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	26,292
Due after Five Years through Ten Years	41,392
Due after Ten Years	1,670,310
Total	1,737,994	1,388,146
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	23,798
Due after Five Years through Ten Years	35,761
Due after Ten Years	1,294,875
Total	1,354,434	1,097,096
Amortized Cost
Due in One Year or Less	99,174
Due after One Year through Five Years	619,010
Due after Five Years through Ten Years	1,092,028
Due after Ten Years	2,139,036
Total	3,949,248
Fair Value
Due in One Year or Less	97,073
Due after One Year through Five Years	587,882
Due after Five Years through Ten Years	914,412
Due after Ten Years	1,669,666
Total	3,269,033
U.S. Treasury
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	14,947
Due after Five Years through Ten Years	0
Due after Ten Years	0
Amortized  Cost	14,947	49,156
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	12,914
Due after Five Years through Ten Years	0
Due after Ten Years	0
Total	12,914	47,017
Agency
Amortized Cost
Due in One Year or Less	80,578
Due after One Year through Five Years	245,493
Due after Five Years through Ten Years	106,631
Due after Ten Years	24,992
Amortized  Cost	457,694	485,331
Fair Value
Due in One Year or Less	78,561
Due after One Year through Five Years	224,454
Due after Five Years through Ten Years	84,760
Due after Ten Years	17,739
Total	405,514	431,438
Corporate
Amortized Cost
Due in One Year or Less	13,000
Due after One Year through Five Years	275,068
Due after Five Years through Ten Years	272,805
Due after Ten Years	0
Amortized  Cost	560,873	586,652
Fair Value
Due in One Year or Less	12,974
Due after One Year through Five Years	270,367
Due after Five Years through Ten Years	221,467
Due after Ten Years	0
Total	504,808	542,548
Collateralized mortgage obligations
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	57,210
Due after Five Years through Ten Years	187,343
Due after Ten Years	92,642
Amortized  Cost	337,195	829,928
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	56,349
Due after Five Years through Ten Years	162,195
Due after Ten Years	85,786
Total	304,330	764,229
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	116
Due after Five Years through Ten Years	0
Due after Ten Years	341,122
Total	341,238
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	116
Due after Five Years through Ten Years	0
Due after Ten Years	324,284
Total	324,400
Mortgage-backed securities
Amortized Cost
Due in One Year or Less	5,596
Due after One Year through Five Years	0
Due after Five Years through Ten Years	483,857
Due after Ten Years	351,092
Amortized  Cost	840,545	953,678
Fair Value
Due in One Year or Less	5,538
Due after One Year through Five Years	0
Due after Five Years through Ten Years	410,229
Due after Ten Years	271,266
Total	687,033	815,781
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	3,489
Due after Ten Years	230,392
Total	233,881	231,692
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	3,395
Due after Ten Years	185,487
Total	188,882	198,071
Municipal bonds
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	26,176
Due after Five Years through Ten Years	37,903
Due after Ten Years	1,082,504
Total	1,146,583	1,148,055
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	23,682
Due after Five Years through Ten Years	32,366
Due after Ten Years	768,812
Total	824,860	$ 890,626
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	16,292
Total	16,292
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	16,292
Total	$ 16,292