Pension and Other Post-Retirement Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0	$ 0
Interest cost	5,597	6,970
Expected return on plan assets	(11,875)	(11,168)
Amortization of net (gain) loss	1,764	941
Net periodic benefit cost (income)	(4,514)	(3,257)
Post-Retirement Healthcare Plans [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	24	35
Interest cost	10	23
Expected return on plan assets	0	0
Amortization of net (gain) loss	47	31
Net periodic benefit cost (income)	$ 81	$ 89