Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			$ 848,324
Other comprehensive income (loss)	$ (10,205)	$ (1,353)	(13,327)	$ (8,462)
Balance, end of period	914,634	826,383	914,634	826,383
AOCI, pension and other postretirement benefit plans, tax benefits (expense)	9,851	9,523	9,851	9,523	$ 9,984	$ 9,563
AOCI, cumulative changes in net gain (loss) from cash flow hedges, tax benefit (expense)	329	(375)	329	(375)	$ (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			(12,262)	(9,901)
Amounts reclassified from accumulated other comprehensive loss			0	0
Other comprehensive income (loss)			(12,262)	(9,901)
Balance, end of period	(42,750)	(27,884)	(42,750)	(27,884)
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			485	131
Other comprehensive income (loss)			485	131
Balance, end of period	(48,215)	(47,067)	(48,215)	(47,067)
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			(1,362)	1,416
Amounts reclassified from accumulated other comprehensive loss			(188)	(108)
Other comprehensive income (loss)			(1,550)	1,308
Balance, end of period	(1,196)	1,334	(1,196)	1,334
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(81,956)	(72,264)	(78,834)	(65,155)
Other comprehensive income (loss) before reclassifications			(13,624)	(8,485)
Amounts reclassified from accumulated other comprehensive loss			297	23
Other comprehensive income (loss)	(10,205)	(1,353)	(13,327)	(8,462)
Balance, end of period	$ (92,161)	$ (73,617)	$ (92,161)	$ (73,617)