Securities - Amortized Cost and Estimated Fair Value by Maturity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in one year or less	$ 11,540
Due after one year through five years	102,806
Due after five years through ten years	73,884
Due after ten years	26,569
Amortized Cost	322,345
Fair Value
Due in one year or less	11,549
Due after one year through five years	102,982
Due after five years through ten years	73,072
Due after ten years	26,212
Fair Value	321,337
Gross realized gains and losses [Abstract]
Realized gains	825	$ 844	$ 871
Realized losses	(13)	(8)	(4)
Other-than-temporary impairment	0	$ 0	$ 0
Mortgage-backed and CMOs
Amortized Cost
Mortgage-backed and CMOs	106,163
Fair Value
Mortgage-backed and CMOs	105,316
Equity securities
Amortized Cost
Equity securities	1,383
Fair Value
Equity securities	$ 2,206