Pensions - Components of Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Interest cost	$ 2,618	$ 4,199	$ 5,234	$ 8,433
Expected return on assets	(2,890)	(4,026)	(5,780)	(8,059)
Settlement (gain)/loss	0	24	(15)	24
Remeasurement (gain)/loss	0	739	(164)	739
Net periodic pension (benefit) cost	$ (272)	$ 936	$ (725)	$ 1,137