Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in One Year or Less	$ 0
Due after One Year through Five Years	500,669
Due after Five Years through Ten Years	1,391,429
Due after Ten Years	1,502,826
Amortized  Cost	3,394,924	$ 4,278,589
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	481,351
Due after Five Years through Ten Years	1,312,217
Due after Ten Years	1,428,527
Total	3,222,095	4,273,864
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	44,774
Due after Ten Years	951,649
Total	996,423	381,696
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	42,509
Due after Ten Years	843,541
Total	886,050	384,423
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	500,669
Due after Five Years through Ten Years	1,436,203
Due after Ten Years	2,454,475
Total	4,391,347
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	481,351
Due after Five Years through Ten Years	1,354,726
Due after Ten Years	2,272,068
Total	4,108,145
U.S. Treasury
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	14,930
Due after Ten Years	0
Amortized  Cost	14,930	57,708
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	13,990
Due after Ten Years	0
Total	13,990	57,866
Agency
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	271,342
Due after Five Years through Ten Years	97,419
Due after Ten Years	37,893
Amortized  Cost	406,654	440,183
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	254,013
Due after Five Years through Ten Years	88,539
Due after Ten Years	33,225
Total	375,777	432,135
Corporate debt
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	192,589
Due after Five Years through Ten Years	405,058
Due after Ten Years	15,000
Amortized  Cost	612,647	451,621
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	190,794
Due after Five Years through Ten Years	389,354
Due after Ten Years	14,917
Total	595,065	453,861
Municipal bonds
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	18,061
Due after Ten Years	427,476
Amortized  Cost	445,537	1,061,985
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	16,806
Due after Ten Years	398,478
Total	415,284	1,089,913
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	44,774
Due after Ten Years	703,113
Total	747,887	368,344
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	42,509
Due after Ten Years	603,580
Total	646,089	370,507
Collateralized mortgage obligations
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	36,738
Due after Five Years through Ten Years	243,674
Due after Ten Years	593,970
Amortized  Cost	874,382	680,686
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	36,544
Due after Five Years through Ten Years	231,495
Due after Ten Years	587,217
Total	855,256	676,643
Mortgage-backed securities
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	612,287
Due after Ten Years	428,487
Amortized  Cost	1,040,774	1,586,406
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	572,033
Due after Ten Years	394,690
Total	966,723	1,563,446
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	247,050
Total	247,050	11,843
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	238,475
Total	238,475	$ 12,407
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	1,486
Total	1,486
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	1,486
Total	$ 1,486