Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income or Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		$ 635,786		$ 584,582		$ 587,281
Actuarial net gain (loss) incurred in fiscal year, net of tax (Note 4)		(1,481)		1,106		2,760
Ending Balance		766,573		635,786		584,582
AOCI, Pension and other postretirement benefit plans, tax		9,563		9,160		9,879
AOCI, Cumulative changes in net gain (loss) from cash flow hedges, tax		15		0		5
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(46,446)		(41,365)
Other comprehensive income before reclassifications		28,463		(5,081)
Actuarial net gain (loss) incurred in fiscal year, net of tax (Note 4)		0		0
Amounts reclassified from accumulated other comprehensive income		0		0
Net current-period other comprehensive income		28,463		(5,081)
Ending Balance		(17,983)		(46,446)		(41,365)
Funded status of pension plans and other postretirement benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	[1]	(45,816)	[2]	(47,082)
Other comprehensive income before reclassifications		0	[2]	0	[1]
Actuarial net gain (loss) incurred in fiscal year, net of tax (Note 4)		(1,481)	[2]	1,106	[1]
Amounts reclassified from accumulated other comprehensive income		99	[2]	160	[1]
Net current-period other comprehensive income		(1,382)	[2]	1,266	[1]
Ending Balance		(47,198)	[2]	(45,816)	[1],[2]	(47,082)	[1]
Unrealized gain (loss) on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	[3]	0	[4]	(11)
Other comprehensive income before reclassifications		26	[4]	0	[3]
Actuarial net gain (loss) incurred in fiscal year, net of tax (Note 4)		0	[4]	0	[3]
Amounts reclassified from accumulated other comprehensive income		0	[4]	11	[3]
Net current-period other comprehensive income		26	[4]	11	[3]
Ending Balance		26	[4]	0	[3],[4]	(11)	[3]
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		(92,262)		(88,458)		(65,094)
Other comprehensive income before reclassifications		28,489		(5,081)
Actuarial net gain (loss) incurred in fiscal year, net of tax (Note 4)		(1,481)		1,106
Amounts reclassified from accumulated other comprehensive income		99		171
Net current-period other comprehensive income		27,107		(3,804)
Ending Balance		$ (65,155)		$ (92,262)		$ (88,458)

[1] Net of taxes of $9,160 and $9,879 for the years ended December 31, 2016 and December 31, 2015, respectively.

[2] Net of taxes of $9,563 and $9,160 for the years ended December 31, 2017 and December 31, 2016, respectively.

[3] Net of taxes of $0 and $5 for the years ended December 31, 2016 and December 31, 2015, respectively.

[4] Net of taxes of $15 and $0 for the years ended December 31, 2017 and December 31, 2016, respectively.