Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost
One Year or Less	$ 496
More than One Year to Five Years	44,282
More than Five Years to Ten Years	481,390
More than Ten Years	700,786
Total	1,226,954	$ 1,111,168
Fair Value
One Year or Less	498
More than One Year to Five Years	46,425
More than Five Years to Ten Years	496,799
More than Ten Years	714,657
Total	1,258,379	1,103,222
Amortized Cost
One Year or Less	0
More than One Year to Five Years	918
More than Five Years to Ten Years	0
More than Ten Years	42,079
Amortized Cost	42,997	45,210
Fair Value
One Year or Less	0
More than One Year to Five Years	962
More than Five Years to Ten Years	0
More than Ten Years	42,697
Total	43,659	44,672
Amortized Cost
One Year or Less	496
More than One Year to Five Years	45,200
More than Five Years to Ten Years	481,390
More than Ten Years	742,865
Total	1,269,951
Fair Value
One Year or Less	498
More than One Year to Five Years	47,387
More than Five Years to Ten Years	496,799
More than Ten Years	757,354
Total	1,302,038
U.S. Treasury
Amortized Cost
One Year or Less	496
More than One Year to Five Years	9,922
More than Five Years to Ten Years	49,327
More than Ten Years	0
Total	59,745	59,688
Fair Value
One Year or Less	498
More than One Year to Five Years	10,405
More than Five Years to Ten Years	52,649
More than Ten Years	0
Total	63,552	60,912
Agency
Amortized Cost
One Year or Less	0
More than One Year to Five Years	32,093
More than Five Years to Ten Years	116,685
More than Ten Years	41,054
Total	189,832	128,958
Fair Value
One Year or Less	0
More than One Year to Five Years	33,694
More than Five Years to Ten Years	122,906
More than Ten Years	42,633
Total	199,233	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	122,755
More than Ten Years	0
Total	122,755	104,158
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	124,119
More than Ten Years	0
Total	124,119	103,543
Municipal bonds
Amortized Cost
One Year or Less	0
More than One Year to Five Years	2,267
More than Five Years to Ten Years	40,211
More than Ten Years	236,484
Total	278,962	238,914
Fair Value
One Year or Less	0
More than One Year to Five Years	2,326
More than Five Years to Ten Years	41,019
More than Ten Years	245,061
Total	288,406	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	2,798
More than Ten Years	16,399
Total	19,197	24,699
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	2,795
More than Ten Years	16,441
Total	19,236	24,338
Mortgage-backed securities: residential
Amortized Cost
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	149,614
More than Ten Years	406,849
Total	556,463	554,751
Fair Value
One Year or Less	0
More than One Year to Five Years	0
More than Five Years to Ten Years	153,311
More than Ten Years	410,522
Total	563,833	545,729
Amortized Cost
One Year or Less	0
More than One Year to Five Years	918
More than Five Years to Ten Years	0
More than Ten Years	40,307
Amortized Cost	41,225	43,381
Fair Value
One Year or Less	0
More than One Year to Five Years	962
More than Five Years to Ten Years	0
More than Ten Years	40,925
Total	41,887	$ 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	1,772
Amortized Cost	1,772
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	1,772
Total	$ 1,772