Retirement Benefits - Pretax Amounts Recognized in Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) in current year	$ (9,963)	$ 5,355	$ 1,927
Amortization of prior service cost (credit)	(2,938)	(3,814)	(7,083)
Total	(12,901)	$ 1,541	$ (5,156)
Pension Benefit Plan | U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) in current year	2,624
Prior service cost	0
Amortization of prior service cost (credit)	24
Amortization of net loss (gain)	2,687
Exchange rate effect on amounts in OCI	0
Total	5,335
Pension Benefit Plan | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) in current year	2,754
Prior service cost	(52)
Amortization of prior service cost (credit)	3
Amortization of net loss (gain)	961
Exchange rate effect on amounts in OCI	746
Total	4,412
Other Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) in current year	3,930
Prior service cost	0
Amortization of prior service cost (credit)	(366)
Amortization of net loss (gain)	(371)
Exchange rate effect on amounts in OCI	(39)
Total	$ 3,154