Securities - Securities with Unrealized Losses - Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Held-to-maturity, Fair Value
Less Than 12 Months	$ 291,456	$ 279,436
12 Months or More	2,483	2,658
Total	293,939	282,094
Held-to-maturity, Unrealized Losses
Less Than 12 Months	(5,040)	(5,554)
12 Months or More	(219)	(244)
Total	(5,259)	(5,798)
Agency mortgage-backed securities
Held-to-maturity, Fair Value
Less Than 12 Months	236,241	222,132
12 Months or More	419	612
Total	236,660	222,744
Held-to-maturity, Unrealized Losses
Less Than 12 Months	(3,282)	(3,528)
12 Months or More	(20)	(26)
Total	(3,302)	(3,554)
Municipals - exempt from Federal tax
Held-to-maturity, Fair Value
Less Than 12 Months	55,215	57,304
12 Months or More	2,064	2,046
Total	57,279	59,350
Held-to-maturity, Unrealized Losses
Less Than 12 Months	(1,758)	(2,026)
12 Months or More	(199)	(218)
Total	(1,957)	$ (2,244)
Municipals - exempt from Federal tax
Held-to-maturity, Fair Value
12 Months or More	$ 2,064