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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plans Disclosure [Line Items]
Interest cost	$ 3,275	$ 4,449	$ 6,550	$ 8,898
Expected return on plan assets	(5,574)	(4,964)	(11,148)	(9,929)
Amortization of actuarial loss	2,849	2,484	5,698	4,968
Total	$ 550	$ 1,969	$ 1,100	$ 3,937