Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance				$ (54,914)		$ (54,914)
Other comprehensive income (loss), Net-of-tax Amount	$ (7,220)		$ (16,261)			6,891	$ (29,313)
Accumulated other comprehensive income (loss), ending balance	(48,023)	$ (54,914)				(48,023)		$ (54,914)
Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance				(16,167)	$ (14,656)	(16,167)	(14,656)	(14,656)
Other comprehensive income (loss) before reclassification						0		(2,307)
Amounts reclassified from accumulated other comprehensive income (loss)						761		796
Other comprehensive income (loss), Net-of-tax Amount						761		(1,511)
Accumulated other comprehensive income (loss), ending balance	(15,406)	(16,167)				(15,406)		(16,167)
Proportionate Share of Telesat Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance				(38,747)	(2,964)	(38,747)	(2,964)	(2,964)
Other comprehensive income (loss) before reclassification						6,130		(35,783)
Amounts reclassified from accumulated other comprehensive income (loss)						0		0
Other comprehensive income (loss), Net-of-tax Amount						6,130		(35,783)
Accumulated other comprehensive income (loss), ending balance	(32,617)	(38,747)				(32,617)		(38,747)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance				(54,914)	(17,620)	(54,914)	$ (17,620)	(17,620)
Other comprehensive income (loss) before reclassification						6,130		(38,090)
Amounts reclassified from accumulated other comprehensive income (loss)						761		796
Other comprehensive income (loss), Net-of-tax Amount	(7,220)	(7,981)	$ (16,261)	$ 14,111	$ (13,052)	6,891		(37,294)
Accumulated other comprehensive income (loss), ending balance	$ (48,023)	$ (54,914)				$ (48,023)		$ (54,914)