Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
One Year or Less	$ 745
More than One Year to Five Years	44,680
More than Five Years to Ten Years	452,633
More than Ten Years	666,282
Total	1,164,340	$ 1,111,168
Fair Value
One Year or Less	745
More than One Year to Five Years	45,995
More than Five Years to Ten Years	458,165
More than Ten Years	666,505
Total	1,171,410	1,103,222
Amortized Cost
One Year or Less	0
More than One Year to Five Years	923
More than Five Years to Ten Years	0
More than Ten Years	42,971
Amortized Cost	43,894	45,210
Fair Value
One Year or Less	0
More than One Year to Five Years	947
More than Five Years to Ten Years	0
More than Ten Years	43,033
Total	43,980	44,672
Amortized Cost
One Year or Less	745
More than One Year to Five Years	45,603
More than Five Years to Ten Years	452,633
More than Ten Years	709,253
Total	1,208,234
Fair Value
One Year or Less	745
More than One Year to Five Years	46,942
More than Five Years to Ten Years	458,165
More than Ten Years	709,538
Total	1,215,390
U.S. Treasury
Amortized Cost
One Year or Less	495
More than One Year to Five Years	9,917
More than Five Years to Ten Years	49,304
More than Ten Years	0
Total	59,716	59,688
Fair Value
One Year or Less	495
More than One Year to Five Years	10,214
More than Five Years to Ten Years	51,192
More than Ten Years	0
Total	61,901	60,912
Agency
Amortized Cost
One Year or Less	0
More than One Year to Five Years	32,098
More than Five Years to Ten Years	84,589
More than Ten Years	45,258
Total	161,945	128,958
Fair Value
One Year or Less	0
More than One Year to Five Years	33,108
More than Five Years to Ten Years	87,279
More than Ten Years	45,101
Total	165,488	130,070
Corporate
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	138,128
More than Ten Years	0
Total	138,128	104,158
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	137,855
More than Ten Years	0
Total	137,855	103,543
Municipal bonds
Amortized Cost
One Year or Less	250
More than One Year to Five Years	2,186
More than Five Years to Ten Years	40,705
More than Ten Years	170,420
Total	213,561	238,914
Fair Value
One Year or Less	250
More than One Year to Five Years	2,202
More than Five Years to Ten Years	40,946
More than Ten Years	173,618
Total	217,016	238,630
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	2,957
More than Ten Years	20,685
Total	23,642	24,699
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	2,916
More than Ten Years	20,535
Total	23,451	24,338
Mortgage-backed securities: residential
Amortized Cost
One Year or Less	0
More than One Year to Five Years	479
More than Five Years to Ten Years	136,950
More than Ten Years	429,919
Total	567,348	554,751
Fair Value
One Year or Less	0
More than One Year to Five Years	471
More than Five Years to Ten Years	137,977
More than Ten Years	427,251
Total	565,699	545,729
Amortized Cost
One Year or Less	0
More than One Year to Five Years	923
More than Five Years to Ten Years	0
More than Ten Years	41,160
Amortized Cost	42,083	43,381
Fair Value
One Year or Less	0
More than One Year to Five Years	947
More than Five Years to Ten Years	0
More than Ten Years	41,222
Total	42,169	$ 42,843
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	1,811
Amortized Cost	1,811
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	1,811
Total	$ 1,811