Pension and Other Post-Retirement Benefits - Schedule of components of net periodic benefit cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 771	$ 733
Interest cost	619	790
Expected return on plan assets	(607)	(626)
Amortization of net loss	541	447
Amortization of prior service (credit)/cost	(194)	(324)
Loss on settlement	4,022	0
Net periodic benefit cost/(credit)	5,152	1,020
U.S. Plans | Defined Benefit
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0	0
Interest cost	267	399
Expected return on plan assets	(433)	(451)
Amortization of net loss	295	245
Amortization of prior service (credit)/cost	0	0
Loss on settlement	4,022	0
Net periodic benefit cost/(credit)	4,151	193
U.S. Plans | Retiree Healthcare
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2	2
Interest cost	37	53
Expected return on plan assets	0	0
Amortization of net loss	10	11
Amortization of prior service (credit)/cost	(196)	(327)
Loss on settlement	0	0
Net periodic benefit cost/(credit)	(147)	(261)
Non-U.S. Plans | Defined Benefit
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	769	731
Interest cost	315	338
Expected return on plan assets	(174)	(175)
Amortization of net loss	236	191
Amortization of prior service (credit)/cost	2	3
Loss on settlement	0	0
Net periodic benefit cost/(credit)	$ 1,148	$ 1,088