Components of Accumulated Other Comprehensive Loss (Details 2) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues		$ 1,503,742	$ 1,347,672	$ 1,307,470
Interest expense		(36,586)	(21,531)	(26,862)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax		27,531	43,942	20,379
Total costs and expenses		1,399,463	1,216,977	1,202,815
Income from continuing operations before income taxes		56,471	113,649	75,402
Income Tax Expense (Benefit)		20,214	5,499	78,190
Net income (loss)		(512,218)	(145,013)	(11,844)
Other Operating Income (Expense), Net		2,621	2,201	$ (7,327)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cumulative Unrecognized Actuarial Losses on Pension Obligations
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total costs and expenses		23,351	20,124
Income Tax Expense (Benefit)		(1,555)	(1,389)
Net income (loss)		21,796	18,735
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of Actuarial Losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		19,806	20,014
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of Prior Service Costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		326	(139)
Cost of services and products sold		3,200	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Settlement/Curtailment Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)		19	249
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Operating Income (Expense), Net		(2,425)	0
Discontinued Operation, Gain From Disposal Of Discontinued Operation, Before Income Tax		$ 662	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Effective Portion of Derivatives Designated as Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income Tax Expense (Benefit)	$ (990)		(147)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign currency exchange forward contracts | Effective Portion of Derivatives Designated as Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	(550)		(374)
Cost of services and products sold	44		0
Income from continuing operations before income taxes	2,934		(218)
Net income (loss)	1,944		(365)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cross-currency interest rate swaps | Effective Portion of Derivatives Designated as Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	(1,219)		(1,264)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest rate swaps | Effective Portion of Derivatives Designated as Hedging Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest expense	520		1,108
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	$ 2,741		$ 0