Investment Securities - By Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Due in One Year or Less	$ 498
Due after One Year through Five Years	68,974
Due after Five Years through Ten Years	534,853
Due after Ten Years	609,878
Total	1,214,203	$ 1,111,168
Fair Value
Due in One Year or Less	499
Due after One Year through Five Years	71,517
Due after Five Years through Ten Years	551,887
Due after Ten Years	632,752
Total	1,256,655	1,103,222
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	913
Due after Five Years through Ten Years	0
Due after Ten Years	39,520
Amortized Cost	40,433	45,210
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	953
Due after Five Years through Ten Years	0
Due after Ten Years	40,349
Total	41,302	44,672
Amortized Cost
Due in One Year or Less	498
Due after One Year through Five Years	69,887
Due after Five Years through Ten Years	534,853
Due after Ten Years	649,398
Total	1,254,636
Fair Value
Due in One Year or Less	499
Due after One Year through Five Years	72,470
Due after Five Years through Ten Years	551,887
Due after Ten Years	673,101
Total	1,297,957
U.S. Treasury
Amortized Cost
Due in One Year or Less	498
Due after One Year through Five Years	20,171
Due after Five Years through Ten Years	39,788
Due after Ten Years	0
Total	60,457	59,688
Fair Value
Due in One Year or Less	499
Due after One Year through Five Years	20,702
Due after Five Years through Ten Years	42,989
Due after Ten Years	0
Total	64,190	60,912
Agency
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	42,658
Due after Five Years through Ten Years	165,240
Due after Ten Years	43,431
Total	251,329	128,958
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	44,453
Due after Five Years through Ten Years	171,635
Due after Ten Years	45,470
Total	261,558	130,070
Corporate
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	125,564
Due after Ten Years	0
Total	125,564	104,158
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	127,802
Due after Ten Years	0
Total	127,802	103,543
Municipal bonds
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	3,569
Due after Five Years through Ten Years	34,911
Due after Ten Years	241,113
Total	279,593	238,914
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	3,710
Due after Five Years through Ten Years	36,057
Due after Ten Years	254,332
Total	294,099	238,630
Collateralized mortgage obligation: residential
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	657
Due after Ten Years	9,857
Total	10,514	24,699
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	652
Due after Ten Years	9,990
Total	10,642	24,338
Mortgage-backed securities: residential
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	2,576
Due after Five Years through Ten Years	168,693
Due after Ten Years	315,477
Total	486,746	554,751
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	2,652
Due after Five Years through Ten Years	172,752
Due after Ten Years	322,960
Total	498,364	545,729
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	913
Due after Five Years through Ten Years	0
Due after Ten Years	37,773
Amortized Cost	38,686	43,381
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	953
Due after Five Years through Ten Years	0
Due after Ten Years	38,602
Total	39,555	$ 42,843
Other
Amortized Cost
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	1,747
Amortized Cost	1,747
Fair Value
Due in One Year or Less	0
Due after One Year through Five Years	0
Due after Five Years through Ten Years	0
Due after Ten Years	1,747
Total	$ 1,747