Pensions - Components of Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Interest cost	$ 3,729	$ 5,537	$ 12,162	$ 16,721
Expected return on assets	(4,001)	(3,761)	(12,060)	(11,259)
Settlement loss	986	719	1,010	719
Remeasurement loss	29,461	13,616	30,200	13,616
Net periodic pension cost	$ 30,175	$ 16,111	$ 31,312	$ 19,797