Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME
Net income (loss)	$ (25,837)	$ 2,755	$ 110	$ 573	$ 5,012	$ 478	$ 2,825	$ 2,199	$ (22,399)	$ 10,514	$ 42,151
Other Comprehensive income (loss):
Currency translation adjustment, net									4,029	(2,488)	(3,292)
Pension adjustment, net of tax of $53 in 2017, $509 in 2016, and $70 in 2015									313	(1,736)	(552)
Comprehensive income (loss)									$ (18,057)	$ 6,290	$ 38,307