Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Due in One Year or Less	$ 10,920
Due after One Year through Five Years	64,852
Due after Five Years through Ten Years	567,220
Due after Ten Years	632,557
Total	1,275,549	$ 1,338,260
Fair Value
Due in One Year or Less	10,626
Due after One Year through Five Years	69,708
Due after Five Years through Ten Years	595,599
Due after Ten Years	661,828
Total	1,337,761	1,368,384
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	34,553
Amortized Cost	34,553	37,838
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	36,238
Total	36,238	38,760
Amortized Cost
Due in One Year or Less	10,920
Due after One Year through Five Years	64,852
Due after Five Years through Ten Years	567,220
Due after Ten Years	667,110
Total	1,310,102
Fair Value
Due in One Year or Less	10,626
Due after One Year through Five Years	69,708
Due after Five Years through Ten Years	595,599
Due after Ten Years	698,066
Total	1,373,999
U.S. Treasury
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	20,155
Due after Five Years through Ten Years	10,024
Due after Ten Years	0
Total	30,179	60,457
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	21,555
Due after Five Years through Ten Years	11,278
Due after Ten Years	0
Total	32,833	63,555
Agency
Amortized Cost
Due in One Year or Less	1,000
Due after One Year through Five Years	40,613
Due after Five Years through Ten Years	155,152
Due after Ten Years	31,950
Total	228,715	240,348
Fair Value
Due in One Year or Less	1,019
Due after One Year through Five Years	43,765
Due after Five Years through Ten Years	166,661
Due after Ten Years	36,321
Total	247,766	246,358
Corporate
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	174,161
Due after Ten Years	0
Total	174,161	149,150
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	176,033
Due after Ten Years	0
Total	176,033	151,353
Municipal bonds
Amortized Cost
Due in One Year or Less	9,920
Due after One Year through Five Years	1,848
Due after Five Years through Ten Years	30,979
Due after Ten Years	349,245
Total	391,992	384,032
Fair Value
Due in One Year or Less	9,607
Due after One Year through Five Years	1,952
Due after Five Years through Ten Years	32,648
Due after Ten Years	362,890
Total	407,097	397,298
Collateralized mortgage obligations
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	566
Due after Ten Years	8,780
Total	9,346	9,869
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	565
Due after Ten Years	9,091
Total	9,656	9,984
Mortgage-backed securities
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	2,236
Due after Five Years through Ten Years	196,338
Due after Ten Years	242,582
Total	441,156	494,404
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	2,436
Due after Five Years through Ten Years	208,414
Due after Ten Years	253,526
Total	464,376	499,836
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	32,865
Amortized Cost	32,865	36,114
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	34,550
Total	34,550	$ 37,036
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	1,688
Amortized Cost	1,688
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	1,688
Total	$ 1,688