Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (37,278)
Net current-period other comprehensive income (loss)	23,831	$ (18,974)
Accumulated other comprehensive income (loss), ending balance	(17,620)	(37,278)
Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(16,454)	(14,074)
Other comprehensive income (loss) before reclassification	953	(1,365)
Amounts reclassified from accumulated other comprehensive income (loss)	845	671
Net current-period other comprehensive income (loss)	1,798	(694)
Accumulated Other Comprehensive Income Tax Cuts and Jobs Act Reclassification to Retained Earnings Tax Effect		(1,686)
Accumulated other comprehensive income (loss), ending balance	(14,656)	(16,454)
Proportionate Share of Telesat Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(20,824)	238
Other comprehensive income (loss) before reclassification	22,033	(18,280)
Net current-period other comprehensive income (loss)	22,033	(18,280)
Accumulated Other Comprehensive Income Tax Cuts and Jobs Act Reclassification to Retained Earnings Tax Effect	(4,173)	(2,782)
Accumulated other comprehensive income (loss), ending balance	(2,964)	(20,824)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(37,278)	(13,836)
Other comprehensive income (loss) before reclassification	22,986	(19,645)
Amounts reclassified from accumulated other comprehensive income (loss)	845	671
Net current-period other comprehensive income (loss)	23,831	(18,974)
Accumulated Other Comprehensive Income Tax Cuts and Jobs Act Reclassification to Retained Earnings Tax Effect	(4,173)	(4,468)
Accumulated other comprehensive income (loss), ending balance	$ (17,620)	$ (37,278)