Components of Accumulated Other Comprehensive Loss Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	$ 9,993	$ 12,405	$ 19,576	$ 24,058
Income from continuing operations before income taxes	44,079	30,562	72,374	47,329
Income tax expense	1,944	11,234	10,210	17,487
Net income	42,711	19,731	62,288	29,868
Amount Reclassified from Accumulated Other Comprehensive Loss | Cumulative Unrecognized Actuarial Losses on Pension Obligations
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes	4,955	5,566	10,224	11,086
Income tax expense	(288)	(522)	(613)	(1,044)
Net income	4,667	5,044	9,611	10,042
Amount Reclassified from Accumulated Other Comprehensive Loss | Effective Portion of Deriviatives Designated as Hedging Instruments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes	245	65	304	308
Income tax expense	(57)	(29)	(207)	(123)
Net income	188	36	97	185
Amount Reclassified from Accumulated Other Comprehensive Loss | Effective Portion of Deriviatives Designated as Hedging Instruments | Foreign currency forward exchange contracts
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Revenues	103	(189)	(109)	(189)
Cost of services and products sold	0	3	0	4
Amount Reclassified from Accumulated Other Comprehensive Loss | Effective Portion of Deriviatives Designated as Hedging Instruments | Cross currency interest rate swaps
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	377	251	648	493
Amount Reclassified from Accumulated Other Comprehensive Loss | Effective Portion of Deriviatives Designated as Hedging Instruments | Interest rate swaps
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Expense	(235)	0	(235)	0
Amount Reclassified from Accumulated Other Comprehensive Loss | Actuarial losses
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	4,992	5,512	10,134	10,979
Amount Reclassified from Accumulated Other Comprehensive Loss | Prior service costs (benefits)
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	(37)	54	(76)	107
Amount Reclassified from Accumulated Other Comprehensive Loss | Settlement/curtailment losses
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	$ 0	$ 0	$ 166	$ 0