Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) [Abstract]
Net income (loss)	$ (40,768)	$ 14,359	$ (20,552)	$ 29,439
Other comprehensive income (loss):
Foreign currency translation adjustments	(8,021)	1,530	(6,309)	3,560
Change in unrecognized pension benefit cost	0	0	65	0
Other comprehensive income (loss)	(8,021)	1,530	(6,244)	3,560
Comprehensive income (loss)	(48,789)	15,889	(26,796)	32,999
Comprehensive loss attributable to non-controlling interest	(237)	(132)	(285)	(124)
Comprehensive income (loss) attributable to controlling interest	$ (48,552)	$ 16,021	$ (26,511)	$ 33,123