Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	$ 848,324
Other comprehensive income (loss)	(4,589)	$ 7,821
Balance, end of period	868,322	799,023
AOCI, pension and other postretirement benefit plans, tax	9,938	9,549	$ 9,984	$ 9,563
AOCI, cumulative changes in net gain (loss) from cash flow hedges, tax	37	(225)	$ (106)	$ (15)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(30,488)	(17,983)
Other comprehensive income (loss) before reclassifications	(4,257)	7,000
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income (loss)	(4,257)	7,000
Balance, end of period	(34,745)	(10,983)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(48,700)	(47,198)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	156	43
Other comprehensive income (loss)	156	43
Balance, end of period	(48,544)	(47,155)
Derivative Instrument Designated as Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	354	26
Other comprehensive income (loss) before reclassifications	(394)	805
Amounts reclassified from accumulated other comprehensive loss	(94)	(27)
Other comprehensive income (loss)	(488)	778
Balance, end of period	(134)	804
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(78,834)	(65,155)
Other comprehensive income (loss) before reclassifications	(4,651)	7,805
Amounts reclassified from accumulated other comprehensive loss	62	16
Other comprehensive income (loss)	(4,589)	7,821
Balance, end of period	$ (83,423)	$ (57,334)