CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 26,136	$ 27,032
Foreign currency translation adjustment	7,000	4,138
Net unrealized gains (losses) on securities:
Net unrealized gain (loss) on marketable securities reclassified into earnings, net of tax (Note 6)	0	0
Derivative instruments designated as cash flow hedges:
Unrealized gain (loss) on derivative instruments held at period end, net of tax (Note 6)	778	(114)
Pension and postretirement benefit plans reclassified into earnings:
Amortization of loss, net of tax (Note 6)	43	30
Other comprehensive income	7,821	4,054
Comprehensive income	$ 33,957	$ 31,086