Pension and Other Post-Retirement Benefits - Pension and Post-Retirement Plans (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Components of net periodic (credit) expense:
Interest cost	[1]	$ 1,173	$ 1,415	$ 3,519	$ 4,245
Expected return on plan assets	[1]	(3,876)	(3,483)	(11,628)	(10,449)
Amortization of net actuarial loss	[1]	1,831	2,509	5,493	7,526
Net periodic (credit) expense	[1]	(872)	441	(2,616)	1,322
Post- Retirement Benefits
Components of net periodic (credit) expense:
Interest cost	[1]	82	128	246	384
Amortization of prior-service costs	[1]	(62)	(62)	(186)	(187)
Amortization of net actuarial loss	[1]	6	31	18	93
Net periodic (credit) expense	[1]	$ 26	$ 97	$ 78	$ 290

[1] Amounts are included in G&A expense on the Consolidated Statements of Income and Comprehensive Income.