Pensions - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Settlement (gain)/loss	$ 0	$ (24)	$ 15	$ (24)
Defined Benefit Plan, Type [Extensible List]	Pension Plan		Pension Plan
Qualified Plan | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution costs	$ 10,000	12,200	$ 15,000	15,800
Expected future employer contribution, current fiscal year	25,000		25,000
Nonqualified Plan | Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution costs	200	$ 200	900	$ 700
Expected future employer contribution, current fiscal year	$ 1,400		$ 1,400