Schedule I - Condensed Financial Information of the Parent (Condensed Statements of Comprehensive Income) (Details) - 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
Condensed Financial Statements, Captions [Line Items]
Other, net									$ (72)	$ 2,151	$ (331)
Other (income) expense									3,712	5,034	3,510
Administrative and general expenses									47,491	48,863	40,105
Income tax benefit									639	(9,649)	(9,510)
Income from continuing operations									28,463	2,956	2,273
Income from discontinued operations									1,874	26,651	19,711
Net income	$ 10,172	$ 8,398	$ 6,789	$ 4,978	$ 24,131	$ (441)	$ 3,115	$ 2,802	30,337	29,607	21,984
Foreign currency translation adjustment									1,725	(2,078)	(2,756)
Deferred gain on available for sale securities, net of tax									834	413	17
Current period cash flow hedging activity, net of $941 tax expense in 2017, $73 tax benefit in 2016 and $357 tax benefit in 2015									1,543	(252)	(577)
Reclassification of hedging activities into earnings, net of $1,255 tax expense in 2017, $419 tax benefit in 2016 and $191 tax benefit in 2015									(2,369)	757	409
Current period pension and postretirement plan adjustment, net of $440 tax expense in 2017, $1,098 tax benefit in 2016 and $1,222 tax benefit in 2015									749	(2,011)	(1,204)
Reclassification of pension and postretirement adjustments into earnings, net of $363 tax benefit in 2017, $408 tax benefit in 2016 and $420 tax benefit in 2015									582	688	856
Total other comprehensive income (loss)									3,064	(2,483)	(3,255)
Comprehensive income									33,401	27,124	18,729
Current period cash flow hedging activity, tax benefit									941	(73)	(357)
Reclassification of hedging activities into earnings, tax benefit									1,255	(419)	(191)
Current period pension and postretirement plan adjustment, tax benefit									440	(1,098)	(1,222)
Reclassification of pension and post retirement adjustments into earnings, tax benefit									(363)	(408)	(420)
Parent Company
Condensed Financial Statements, Captions [Line Items]
Intercompany interest expense									1,256	1,285	1,309
Other, net									(314)	(332)	(270)
Other (income) expense									942	953	1,039
Administrative and general expenses									6,466	6,881	3,704
Income (loss) from continuing operations before income tax provision (benefit)									(7,408)	(7,834)	(4,743)
Income tax benefit									(366)	(2,295)	(1,496)
Net loss before equity in earnings of subsidiaries									(7,042)	(5,539)	(3,247)
Equity in earnings of subsidiaries									35,505	8,495	5,520
Income from continuing operations									28,463	2,956	2,273
Income from discontinued operations									1,874	26,651	19,711
Net income									30,337	29,607	21,984
Foreign currency translation adjustment									1,725	(2,078)	(2,756)
Deferred gain on available for sale securities, net of tax									834	413	17
Current period cash flow hedging activity, net of $941 tax expense in 2017, $73 tax benefit in 2016 and $357 tax benefit in 2015									1,543	(252)	(577)
Reclassification of hedging activities into earnings, net of $1,255 tax expense in 2017, $419 tax benefit in 2016 and $191 tax benefit in 2015									(2,369)	757	409
Current period pension and postretirement plan adjustment, net of $440 tax expense in 2017, $1,098 tax benefit in 2016 and $1,222 tax benefit in 2015									749	(2,011)	(1,204)
Reclassification of pension and postretirement adjustments into earnings, net of $363 tax benefit in 2017, $408 tax benefit in 2016 and $420 tax benefit in 2015									582	688	856
Total other comprehensive income (loss)									3,064	(2,483)	(3,255)
Comprehensive income									33,401	27,124	18,729
Current period cash flow hedging activity, tax benefit									941	(73)	(357)
Reclassification of hedging activities into earnings, tax benefit									1,255	(419)	(191)
Current period pension and postretirement plan adjustment, tax benefit									440	(1,098)	(1,222)
Reclassification of pension and post retirement adjustments into earnings, tax benefit									$ (363)	$ (408)	$ (420)