Pension Benefits, Other Postretirement Benefits and Employee Savings and Investment Plans (Amounts Recognized in Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets & Liabilities:
Non-current assets	$ 5,278	$ 12,790
Pension Benefits
Assets & Liabilities:
Non-current assets	5,278	12,790
Current liabilities	(14)	(5)
Non-current liabilities	(257)	(250)
Net assets (liabilities)	5,007	12,535
Accumulated Other Comprehensive Loss:
Net actuarial (loss) gain	(11,171)	(13,085)
Prior service benefit	0	0
Accumulated other comprehensive (loss) income	(11,171)	(13,085)
Other Postretirement Benefits
Assets & Liabilities:
Non-current assets	0	0
Current liabilities	(148)	(282)
Non-current liabilities	(1,355)	(1,317)
Net assets (liabilities)	(1,503)	(1,599)
Accumulated Other Comprehensive Loss:
Net actuarial (loss) gain	119	54
Prior service benefit	97	209
Accumulated other comprehensive (loss) income	$ 216	$ 263