Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 14,359	$ 18,141	$ 29,439	$ 35,819
Other comprehensive income (loss):
Income tax benefit on change in unrecognized pension and post-retirement benefit costs	0	(111)	0	(111)
Foreign currency translation adjustments	1,530	(2,017)	3,560	(287)
Income tax provision on foreign currency translation adjustments	0	(394)	0	(728)
Other comprehensive income (loss)	1,530	(2,522)	3,560	(1,126)
Comprehensive income	15,889	15,619	32,999	34,693
Comprehensive income (loss) attributable to non-controlling interest	(132)	14	(124)	74
Comprehensive income attributable to controlling interest	$ 16,021	$ 15,605	$ 33,123	$ 34,619