CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Issuance of common shares per stock based compensation awards, including related tax effects, shares	61,899	118,559	118,281
Common stock acquired for treasury, shares	900	270,378	338,985
Common stock dividend (in dollars per share)	$ 0.76	$ 0.720	$ 0.671
Cash Paid in Lieu of Fractional Shares			$ 13