Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Consolidated Statements Of Stockholders' Equity [Abstract]
Dividends declared per share	$ 0.17	$ 0.14
Common stock grants to directors, shares	6,731	5,156
Unearned compensation expense	$ 503	$ 403
Shares issued under employee stock purchase plan, shares	1,663	1,830
Treasury stock, shares, acquired		6,557
Purchased treasury stock, price per share		$ 14.80