Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) [Abstract]
Net income (loss)	$ 6,903	$ (2,703)	$ (13,649)	$ 26,736
Other comprehensive income (loss):
Foreign currency translation adjustments	(1,536)	1,346	(7,845)	4,906
Change in unrecognized pension benefit cost	0	0	65	0
Other comprehensive income (loss)	(1,536)	1,346	(7,780)	4,906
Comprehensive income (loss)	5,367	(1,357)	(21,429)	31,642
Comprehensive income (loss) attributable to non-controlling interest	(122)	8	(407)	(117)
Comprehensive income (loss) attributable to controlling interest	$ 5,489	$ (1,365)	$ (21,022)	$ 31,759