Pensions - Schedule of Fair Value of Pension Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	$ 444,228	$ 449,019	$ 424,927
Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	312,298	324,874
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	17,831	8,029
Fair Value, Inputs, Level 1, 2 and 3 | Equity funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	88,118	99,963
Fair Value, Inputs, Level 1, 2 and 3 | U.S. treasuries and agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	35,797	29,610
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bond funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	170,552	187,272
Level 1 (quoted market prices in active markets)
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	276,501	295,264
Level 1 (quoted market prices in active markets) | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	17,831	8,029
Level 1 (quoted market prices in active markets) | Equity funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	88,118	99,963
Level 1 (quoted market prices in active markets) | U.S. treasuries and agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 1 (quoted market prices in active markets) | Corporate bond funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	170,552	187,272
Level 2 (significant observable input)
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	35,797	29,610
Level 2 (significant observable input) | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 2 (significant observable input) | Equity funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 2 (significant observable input) | U.S. treasuries and agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	35,797	29,610
Level 2 (significant observable input) | Corporate bond funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 3 (Unobservable inputs)
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 3 (Unobservable inputs) | Cash and cash equivalents
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 3 (Unobservable inputs) | Equity funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 3 (Unobservable inputs) | U.S. treasuries and agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Level 3 (Unobservable inputs) | Corporate bond funds
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	0	0
Hedge funds-investments measured at NAV as a practical expedient
Defined Benefit Plan, Plan Assets, Category [Line Items]
Total plan assets	$ 131,930	$ 124,145