Pension and Other Post-Retirement Benefits - Components of Pension Expense and Other Postretirement Benefit Expense (Details) - Pension Plans, Defined Benefit - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans Disclosure [Line Items]
Interest cost	$ 3,321	$ 4,552	$ 9,871	$ 13,450
Expected return on plan assets	(4,930)	(4,995)	(16,078)	(14,924)
Amortization of actuarial loss	2,871	2,708	8,569	7,676
Total	$ 1,262	$ 2,265	$ 2,362	$ 6,202