CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Net income	$ 37,590	$ 54,988	$ 31,966
Other comprehensive income (loss):
Change in unrecognized pension and post-retirement benefit costs	689	(80)	(178)
Tax (expense) benefit on change in unrecognized pension and post-retirement benefit costs	(69)	29	36
Foreign currency translation adjustments	6,699	(2,420)	(13,848)
Tax (expense) benefit on foreign currency translation adjustments	0	(5,527)	3,341
Other comprehensive income (loss)	7,319	(7,998)	(10,649)
Comprehensive loss attributable to non-controlling interest	(232)	(137)	(1,603)
Comprehensive income attributable to controlling interest	$ 45,141	$ 47,127	$ 22,920