Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 72,793	$ 108,787	$ 103,409
Other comprehensive income (loss), net of tax:
Currency translation adjustments (net of income tax of $0 in 2017, 2016 and 2015)	43,060	(15,017)	(27,581)
Change in unrecognized net periodic pension costs (net of income tax of $6 in 2017, $343 in 2016, and $90 in 2015)	(857)	(727)	(159)
Other (net of income tax of $0 in 2017, 2016, and 2015)	196	86	(84)
Other comprehensive income (loss)	42,399	(15,658)	(27,824)
Comprehensive income	$ 115,192	$ 93,129	$ 75,585