Retirement Benefits - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) employee	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized		$ 0	$ 0	$ 3,554
Accumulated benefit obligation for all defined benefit pension plans		$ 169,500	182,700
Percentage of excess gains and losses over benefit obligation or market value of assets amortized		10.00%
Costs of defined contribution plans		$ 12,200	10,200	10,100
Number of participants covering under multi employer pension plan | employee		343
Costs of bargaining unit-sponsored multi-employer plans and defined contribution plans		$ 1,100	1,000	1,300
Weighted average annual rate of increase in the per capita cost of covered health care benefits assumed		6.04%
Assumed decrease of weighted average health care cost trend rate		4.50%
Year that reaches assumed decrease of weighted average health care cost trend rate		2038
Increase in service and interest cost components of the net periodic benefit cost, as 1% increase in health care cost trend rates		$ 200
Increase in accumulated postretirement benefit obligation, as 1% increase in health care cost trend rates		1,900
Decrease in service and interest cost components of the net periodic benefit cost, as 1% decrease in health care cost trend rates		100
Decrease in accumulated postretirement benefit obligation, as 1% decrease in health care cost trend rates		1,600
Future estimated benefit payments for year 2019		11,400
Future estimated benefit payments for year 2020		11,500
Future estimated benefit payments for year 2021		11,300
Future estimated benefit payments for year 2022		11,000
Future estimated benefit payments for year 2023		10,900
Future estimated benefit payments for years 2024 to 2027		54,300
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year		12,000
401k
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year		$ 9,700
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		10.00%
Equity Securities | UK
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		40.00%
Equity Securities | UK | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		40.00%
Equity Securities | UK | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		50.00%
Fixed Income Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		90.00%
Fixed Income Securities | UK
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		60.00%
Fixed Income Securities | UK | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		50.00%
Fixed Income Securities | UK | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		60.00%
Pension Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contribution for next fiscal year		$ 600
Pension Benefit Plan | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment			0	11,000
Settlement loss recognized	$ 3,500	(1)	0	3,339
Pension Benefit Plan | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment		2,313	2,452
Settlement loss recognized		$ (307)	234	$ 215
Pension Benefit Plan | Non-U.S. Plans | UK
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities		2.00%
Other Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment		$ 0	$ 0
Defined benefit plan, expected contribution for next fiscal year		$ 1,100