Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (54,914)
Other comprehensive income (loss), Net-of-tax Amount	(17,058)	$ (37,294)
Accumulated other comprehensive income (loss), ending balance	(71,972)	(54,914)
Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(16,167)	(14,656)
Other comprehensive income (loss) before reclassification	(3,852)	(2,307)
Amounts reclassified from accumulated other comprehensive income (loss)	1,026	796
Other comprehensive income (loss), Net-of-tax Amount	(2,826)	(1,511)
Accumulated other comprehensive income (loss), ending balance	(18,993)	(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)
Other comprehensive income (loss) before reclassification	(14,232)	(35,783)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Other comprehensive income (loss), Net-of-tax Amount	(14,232)	(35,783)
Accumulated other comprehensive income (loss), ending balance	(52,979)	(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)
Other comprehensive income (loss) before reclassification	(18,084)	(38,090)
Amounts reclassified from accumulated other comprehensive income (loss)	1,026	796
Other comprehensive income (loss), Net-of-tax Amount	(17,058)	(37,294)
Accumulated other comprehensive income (loss), ending balance	$ (71,972)	$ (54,914)