Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized Cost
One Year or Less	$ 3,806
More than One Year to Five Years	38,142
More than Five Years to Ten Years	300,153
More than Ten Years	549,962
Total	892,063	$ 786,783
Fair Value
One Year or Less	3,807
More than One Year to Five Years	38,040
More than Five Years to Ten Years	295,613
More than Ten Years	537,240
Total	874,700	787,429
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	31,965
Amortized Cost	31,965	18,291
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	31,127
Total	31,127	18,082
Amortized Cost
One Year or Less	3,806
More than One Year to Five Years	38,142
More than Five Years to Ten Years	300,153
More than Ten Years	581,927
Total	924,028
Fair Value
One Year or Less	3,807
More than One Year to Five Years	38,040
More than Five Years to Ten Years	295,613
More than Ten Years	568,367
Total	905,827
Agency
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	18,560
More than Ten Years	23,007
Total	41,567	47,051
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	18,371
More than Ten Years	22,706
Total	41,077	47,209
Corporate
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	93,126
More than Ten Years	0
Total	93,126	78,155
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	92,502
More than Ten Years	0
Total	92,502	79,546
Municipal bonds
Amortized Cost
One Year or Less	3,806
More than One Year to Five Years	36,076
More than Five Years to Ten Years	68,094
More than Ten Years	113,830
Total	221,806	228,929
Fair Value
One Year or Less	3,807
More than One Year to Five Years	36,038
More than Five Years to Ten Years	66,741
More than Ten Years	113,315
Total	219,901	232,128
Collateralized mortgage obligation: residential
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	934
More than Ten Years	28,813
Total	29,747	33,984
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	936
More than Ten Years	28,222
Total	29,158	33,781
Mortgage-backed securities: residential
Amortized Cost
One Year or Less	0
More than One Year to Five Years	2,066
More than Five Years to Ten Years	119,439
More than Ten Years	384,312
Total	505,817	398,664
Fair Value
One Year or Less	0
More than One Year to Five Years	2,002
More than Five Years to Ten Years	117,063
More than Ten Years	372,997
Total	492,062	394,765
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	30,854
Amortized Cost	30,854	17,153
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	30,016
Total	30,016	$ 16,944
Other
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	1,111
Amortized Cost	1,111
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	0
More than Ten Years	1,111
Total	$ 1,111