Pensions - Components of Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Interest cost	$ 2,617	$ 3,729	$ 7,851	$ 12,162
Expected return on assets	(2,890)	(4,001)	(8,670)	(12,060)
Settlement (gain)/loss	0	986	(15)	1,010
Remeasurement (gain)/loss	0	29,461	(164)	30,200
Net periodic pension (benefit) cost	$ (273)	$ 30,175	$ (998)	$ 31,312