Securities, AFS Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2018 USD ($) Position	Dec. 31, 2017 USD ($) Position
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 432,784	$ 633,766
12 months or longer	623,003	386,818
Total	1,055,787	1,020,584
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(11,908)	(5,481)
12 months or longer	(29,224)	(10,652)
Total	$ (41,132)	$ (16,133)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	114	134
12 months or longer | Position	147	79
Total | Position	261	213
Federal Agency [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 39,069	$ 64,653
12 months or longer	44,193	44,246
Total	83,262	108,899
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(916)	(242)
12 months or longer	(796)	(721)
Total	$ (1,712)	$ (963)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	4	5
12 months or longer | Position	4	4
Total | Position	8	9
State & Municipal [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 12,347	$ 23,566
12 months or longer	16,165	5,994
Total	28,512	29,560
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(115)	(200)
12 months or longer	(272)	(77)
Total	$ (387)	$ (277)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	22	39
12 months or longer | Position	25	8
Total | Position	47	47
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 297,802	$ 317,630
12 months or longer	178,186	58,316
Total	475,988	375,946
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(9,061)	(2,381)
12 months or longer	(8,215)	(1,187)
Total	$ (17,276)	$ (3,568)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	72	55
12 months or longer | Position	48	24
Total | Position	120	79
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 83,566	$ 227,917
12 months or longer	384,459	275,303
Total	468,025	503,220
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,816)	(2,658)
12 months or longer	(19,941)	(8,521)
Total	$ (21,757)	$ (11,179)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	16	35
12 months or longer | Position	70	42
Total | Position	86	77
Equity Securities [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 0
12 months or longer		2,959
Total		2,959
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months		0
12 months or longer		(146)
Total		$ (146)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position		0
12 months or longer | Position		1
Total | Position		1