Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended			12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance		$ (17,620)			$ (17,620)
Other comprehensive income (loss), Net-of-tax Amount	$ (6,646)		$ 628		(13,052)		$ 7,772
Accumulated other comprehensive income (loss), ending balance	(30,672)				(30,672)	$ (17,620)		$ (17,620)
Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance		(14,656)		$ (16,454)	(14,656)		(16,454)	(16,454)
Other comprehensive income (loss) before reclassification								953
Amounts reclassified from accumulated other comprehensive income (loss)					395			845
Other comprehensive income (loss), Net-of-tax Amount					395			1,798
Accumulated other comprehensive income (loss), ending balance	(14,261)				(14,261)	(14,656)		(14,656)
Proportionate Share of Telesat Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance		(2,964)		(20,824)	(2,964)		(20,824)	(20,824)
Other comprehensive income (loss) before reclassification					(13,447)			22,033
Amounts reclassified from accumulated other comprehensive income (loss)
Other comprehensive income (loss), Net-of-tax Amount					(13,447)			22,033
Tax Cuts and Jobs Act, reclassification of tax effect from accumulated other comprehensive loss to accumulated deficit								(4,173)
Accumulated other comprehensive income (loss), ending balance	(16,411)				(16,411)	(2,964)		(2,964)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance		(17,620)		(37,278)	(17,620)		$ (37,278)	(37,278)
Other comprehensive income (loss) before reclassification					(13,447)			22,986
Amounts reclassified from accumulated other comprehensive income (loss)					395			845
Other comprehensive income (loss), Net-of-tax Amount	(6,646)	$ (6,406)	$ 628	$ 7,144	(13,052)	16,059		23,831
Tax Cuts and Jobs Act, reclassification of tax effect from accumulated other comprehensive loss to accumulated deficit								(4,173)
Accumulated other comprehensive income (loss), ending balance	$ (30,672)				$ (30,672)	$ (17,620)		$ (17,620)