CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Stockholders' Equity [Abstract]
Net unrealized holding gains (losses) arising during period, tax effect	$ 44	$ 440	$ 83
Common stock, dividends, per share, cash paid	$ 0.40	$ 0.40	$ 0.40