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]
Tax effect of unrealized gain on derivative instruments	$ (5)	$ (22)	$ 22
Tax effect of unrealized gain on available-for-sale investments	2	248	(279)
Tax benefit of foreign currency translation adjustment	$ 0	$ (228)	$ (711)