Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost
One Year or Less	$ 7,035
More than One Year to Five Years	33,603
More than Five Years to Ten Years	279,078
More than Ten Years	556,089
Total	875,805	$ 786,783
Fair Value
One Year or Less	7,028
More than One Year to Five Years	33,477
More than Five Years to Ten Years	276,674
More than Ten Years	546,064
Total	863,243	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	24,559
Amortized Cost	24,559	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	23,915
Total	23,915	18,082
Amortized Cost
One Year or Less	7,035
More than One Year to Five Years	33,603
More than Five Years to Ten Years	279,078
More than Ten Years	580,648
Total	900,364
Fair Value
One Year or Less	7,028
More than One Year to Five Years	33,477
More than Five Years to Ten Years	276,674
More than Ten Years	569,979
Total	887,158
Agency
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	19,761
More than Ten Years	24,447
Total	44,208	47,051
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	19,726
More than Ten Years	24,438
Total	44,164	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	91,671
More than Ten Years	12,000
Total	103,671	78,155
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	92,330
More than Ten Years	12,076
Total	104,406	79,546
Municipal bonds
Amortized Cost
One Year or Less	4,463
More than One Year to Five Years	31,257
More than Five Years to Ten Years	73,327
More than Ten Years	116,154
Total	225,201	228,929
Fair Value
One Year or Less	4,463
More than One Year to Five Years	31,194
More than Five Years to Ten Years	72,004
More than Ten Years	115,996
Total	223,657	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	1,007
More than Ten Years	31,216
Total	32,223	33,984
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	1,009
More than Ten Years	30,700
Total	31,709	33,781
Mortgage-backed securities: residential
Amortized Cost
One Year or Less	2,572
More than One Year to Five Years	2,346
More than Five Years to Ten Years	93,312
More than Ten Years	372,272
Total	470,502	398,664
Fair Value
One Year or Less	2,565
More than One Year to Five Years	2,283
More than Five Years to Ten Years	91,605
More than Ten Years	362,854
Total	459,307	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	23,434
Amortized Cost	23,434	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	22,790
Total	22,790	$ 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	1,125
Amortized Cost	1,125
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	1,125
Total	$ 1,125