Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	$ 1,020,755
Other comprehensive income (loss) before reclassifications	(13,259)	$ (8,143)
Amounts reclassified from accumulated other comprehensive loss	63	(1)
Other comprehensive income (loss)	(13,196)	(8,144)
Balance, end of period	1,040,855	937,809
AOCI, Pension and other postretirement benefit plans, tax	1,940	2,349	$ 1,951	$ 2,368
AOCI, cumulative changes in net gain (loss) from cash flow hedges, tax	0	656	$ 0	$ 282
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(19,575)	(46,905)
Other comprehensive income (loss)	(13,196)	(8,144)
Balance, end of period	(32,771)	(55,049)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(10,571)	(35,478)
Other comprehensive income (loss) before reclassifications	(13,259)	(6,894)
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive income (loss)	(13,259)	(6,894)
Balance, end of period	(23,830)	(42,372)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(9,004)	(10,455)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	63	66
Other comprehensive income (loss)	63	66
Balance, end of period	(8,941)	(10,389)
Derivative Instrument Designated as Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	0	(972)
Other comprehensive income (loss) before reclassifications	0	(1,249)
Amounts reclassified from accumulated other comprehensive loss	0	(67)
Other comprehensive income (loss)	0	(1,316)
Balance, end of period	$ 0	$ (2,288)