Investment Securities - Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value
Less than 12 Months	$ 202,036	$ 305,174
12 Months or Longer	432,404	183,711
Total	634,440	488,885
Unrealized Losses
Less than 12 Months	(823)	(2,448)
12 Months or Longer	(11,908)	(4,679)
Total	(12,731)	(7,127)
U.S. Treasury and U.S. Government-sponsored agencies
Fair Value
Less than 12 Months	46,992	11,436
12 Months or Longer	7,350	0
Total	54,342	11,436
Unrealized Losses
Less than 12 Months	(58)	(24)
12 Months or Longer	(89)	0
Total	(147)	(24)
Municipal securities
Fair Value
Less than 12 Months	31,157	39,298
12 Months or Longer	38,792	26,509
Total	69,949	65,807
Unrealized Losses
Less than 12 Months	(159)	(384)
12 Months or Longer	(647)	(679)
Total	(806)	(1,063)
Residential mortgage-backed securities
Fair Value
Less than 12 Months	66,620	175,847
12 Months or Longer	193,726	66,380
Total	260,346	242,227
Unrealized Losses
Less than 12 Months	(247)	(1,296)
12 Months or Longer	(5,872)	(1,639)
Total	(6,119)	(2,935)
Commercial mortgage-backed securities
Fair Value
Less than 12 Months	43,531	75,121
12 Months or Longer	190,585	90,822
Total	234,116	165,943
Unrealized Losses
Less than 12 Months	(272)	(700)
12 Months or Longer	(5,252)	(2,361)
Total	(5,524)	(3,061)
Corporate obligations
Fair Value
Less than 12 Months	13,736	3,472
12 Months or Longer	1,951	0
Total	15,687	3,472
Unrealized Losses
Less than 12 Months	(87)	(44)
12 Months or Longer	(48)	0
Total	$ (135)	$ (44)