Components of Accumulated Other Comprehensive Loss (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Revenues	$ 1,863,864	$ 1,503,742	$ 1,347,672
Interest expense	(59,689)	(36,586)	(21,531)
Income (loss) from discontinued business	(2,745)	27,531	43,942
Total costs and expenses	1,842,783	1,399,463	1,216,977
Income from continuing operations before income taxes	(31,125)	56,471	113,649
Income Tax Expense (Benefit)	(2,779)	20,214	5,499
Net income (loss)	21,975	(512,218)	(145,013)
Other Operating Income (Expense), Net	(10,794)	2,621	$ 2,201
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	25,405	23,351
Income Tax Expense (Benefit)	(2,659)	(1,555)
Net income (loss)	22,746	21,796
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension asset transfer - discontinued businesses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cost of services and products sold	5,363	3,200
Reclassification out of Accumulated Other Comprehensive Income [Member] | Settlement/curtailment losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	(92)	19
Reclassification out of Accumulated Other Comprehensive Income [Member] | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	19,623	19,806
Other Operating Income (Expense), Net	12,906	(2,425)
Discontinued Operation, Gain From Disposal Of Discontinued Operation, Before Income Tax	0	662
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)	(992)	(990)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	511	326
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	(1,026)	(550)
Cost of services and products sold	0	44
Income from continuing operations before income taxes	2,578	2,934
Net income (loss)	1,586	1,944
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	(1,015)	(1,219)
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	(2,589)	520
Income (loss) from discontinued business	$ 0	$ 2,741