Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost
One Year or Less	$ 7,206
More than One Year to Five Years	37,551
More than Five Years to Ten Years	203,178
More than Ten Years	451,818
Total	699,753	$ 385,662
Fair Value
One Year or Less	7,201
More than One Year to Five Years	37,864
More than Five Years to Ten Years	205,461
More than Ten Years	453,418
Total	703,944	380,963
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	18,627
Amortized Cost	18,627	8,565
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	18,577
Total	18,577	8,461
Amortized Cost
One Year or Less	7,206
More than One Year to Five Years	37,551
More than Five Years to Ten Years	203,178
More than Ten Years	470,445
Total	718,380
Fair Value
One Year or Less	7,201
More than One Year to Five Years	37,864
More than Five Years to Ten Years	205,461
More than Ten Years	471,995
Total	722,521
Agency
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	16,085
More than Ten Years	33,884
Total	49,969
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	16,176
More than Ten Years	34,203
Total	50,379
Corporate
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	56,040
More than Ten Years	5,000
Total	61,040	37,475
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	57,175
More than Ten Years	5,000
Total	62,175	37,642
Municipal bonds
Amortized Cost
One Year or Less	4,592
More than One Year to Five Years	32,249
More than Five Years to Ten Years	72,854
More than Ten Years	114,637
Total	224,332	120,155
Fair Value
One Year or Less	4,598
More than One Year to Five Years	32,569
More than Five Years to Ten Years	73,907
More than Ten Years	117,353
Total	228,427	118,803
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	3,361
More than Ten Years	39,893
Total	43,254	31,536
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	3,406
More than Ten Years	39,998
Total	43,404	31,388
Mortgage-backed securities: residential
Amortized Cost
One Year or Less	2,614
More than One Year to Five Years	5,302
More than Five Years to Ten Years	54,838
More than Ten Years	258,404
Total	321,158	196,496
Fair Value
One Year or Less	2,603
More than One Year to Five Years	5,295
More than Five Years to Ten Years	54,797
More than Ten Years	256,864
Total	319,559	193,130
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	17,476
Amortized Cost	17,476	7,375
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	17,426
Total	17,426	$ 7,271
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	1,151
Amortized Cost	1,151
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	1,151
Total	$ 1,151