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, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 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	$ (16,261)		$ (5,410)			(29,313)	$ 2,362
Accumulated other comprehensive income (loss), ending balance	(46,933)	$ (17,620)				(46,933)		$ (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)						594		845
Other comprehensive income (loss), Net-of-tax Amount						594		1,798
Accumulated other comprehensive income (loss), ending balance	(14,062)	(14,656)				(14,062)		(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						(7,857)		22,033
Amounts reclassified from accumulated other comprehensive income (loss)
Other comprehensive income (loss), Net-of-tax Amount						(29,907)		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	(32,871)	(2,964)				(32,871)		(2,964)
Proportionate Share of Telesat Other Comprehensive Loss [Member] | Restatement Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification						(22,050)
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						(7,857)		22,986
Amounts reclassified from accumulated other comprehensive income (loss)						594		845
Other comprehensive income (loss), Net-of-tax Amount	(16,261)	21,469	$ (5,410)	$ (13,052)	$ 7,772	(29,313)		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	$ (46,933)	$ (17,620)				(46,933)		$ (17,620)
Accumulated Other Comprehensive Loss [Member] | Restatement Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) before reclassification						$ (22,050)