Pensions - Components of Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Retirement Benefits [Abstract]
Interest cost	$ 2,616	$ 4,234
Expected return on assets	(2,890)	(4,033)
Settlement (gain)	(15)	0
Remeasurement (gain)	(164)	0
Net periodic pension (benefit) cost	$ (453)	$ 201