CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF EQUITY
Issuance of restricted shares of common stock	95,095	100,005	93,864
Issuance of shares of common stock upon exercise of stock options	35,081	43,053	87,378
Purchase of shares of common stock	234,746	70,686	37,567
Other comprehensive income, tax	$ 679	$ 677	$ 717