Retirement Benefits - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) shares	Dec. 31, 2019 USD ($) employee shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2019 employee
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for all defined benefit pension plans	$ 193,300	$ 193,300	$ 169,500
Percentage of excess gains and losses over benefit obligation or market value of assets amortized		10.00%
Costs of defined contribution plans		$ 12,400	12,200	$ 10,200
Number of participants covering under multi employer pension plan | employee		259
Costs of bargaining unit-sponsored multi-employer plans and defined contribution plans		$ 1,100	1,100	1,000
Weighted average annual rate of increase in the per capita cost of covered health care benefits assumed	5.84%	5.84%
Assumed decrease of weighted average health care cost trend rate		4.45%
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		$ 100
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
Stock held in plan assets (in shares) | shares	0	0
Estimated Future Benefit Payments
2020	$ 49,400	$ 49,400
2021	49,200	49,200
2022	5,700	5,700
2023	5,600	5,600
2024	5,900	5,900
2025 to 2029	$ 30,700	30,700
Defined Contribution Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year		12,800
401k
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, expected contribution for next fiscal year		$ 10,200
U.S. | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	10.00%	10.00%
U.S. | Fixed Income Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	90.00%	90.00%
UK | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	40.00%	40.00%
UK | Equity Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	40.00%	40.00%
UK | Equity Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	50.00%	50.00%
UK | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	60.00%	60.00%
UK | Fixed Income Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	50.00%	50.00%
UK | Fixed Income Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	60.00%	60.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement loss recognized	$ 700
Participants affected due to plan freeze | employee					60
Reduction in liabilities	1,200	$ 1,200
Defined benefit plan, expected contribution for next fiscal year	$ 3,000	3,000
Pension Benefits | U.S.
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment		4,826	0
Settlement loss recognized		713	(1)	0
Pension Benefits | Non-U.S.
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment		0	2,313
Settlement loss recognized		$ 0	(307)	$ 234
Pension Benefits | UK
Defined Benefit Plan Disclosure [Line Items]
Target allocation of fund assets in equities	2.50%	2.50%
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Lump sum payment		$ 0	$ 0
Defined benefit plan, expected contribution for next fiscal year	$ 1,100	$ 1,100