Securities, AFS Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2019 USD ($) Position	Dec. 31, 2018 USD ($) Position
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 36,973	$ 32,295
12 months or longer	673,598	835,966
Total	710,571	868,261
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(168)	(137)
12 months or longer	(10,164)	(20,209)
Total	$ (10,332)	$ (20,346)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	7	20
12 months or longer | Position	155	204
Total | Position	162	224
Federal Agency [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 0	$ 0
12 months or longer	9,636	64,294
Total	9,636	64,294
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	0	0
12 months or longer	(364)	(693)
Total	$ (364)	$ (693)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	0	0
12 months or longer | Position	1	6
Total | Position	1	6
State & Municipal [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months		$ 1,715
12 months or longer		22,324
Total		24,039
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months		(3)
12 months or longer		(234)
Total		$ (237)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position		3
12 months or longer | Position		35
Total | Position		38
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 234	$ 18,462
12 months or longer	352,339	428,440
Total	352,573	446,902
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(2)	(65)
12 months or longer	(4,328)	(10,764)
Total	$ (4,330)	$ (10,829)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	2	12
12 months or longer | Position	90	101
Total | Position	92	113
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	$ 36,739	$ 12,118
12 months or longer	311,623	320,908
Total	348,362	333,026
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(166)	(69)
12 months or longer	(5,472)	(8,518)
Total	$ (5,638)	$ (8,587)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	5	5
12 months or longer | Position	64	62
Total | Position	69	67