Consolidated Statements of Changes in Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Stockholders Equity [Abstract]
Amortization of terminated hedge, income tax effect		$ 60	$ 120
Unrealized loss on marketable security, income tax effect	$ (809)	(831)
Unrealized derivative gains and losses on cash flow hedges, income tax effect	2,490	536	2,283
Minimum pension liability, income tax effect	$ (983)	$ (5,003)	$ (817)