Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Accumulated other comprehensive income (loss), beginning balance	$ (13,836)
Net current-period other comprehensive income (loss)	(3,038)	$ 9,159
Accumulated other comprehensive income (loss), ending balance	(16,874)		$ (13,836)
Postretirement Benefits [Member]
Accumulated other comprehensive income (loss), beginning balance	(14,074)	(13,459)	(13,459)
Other comprehensive income (loss) before reclassification			(1,209)
Amounts reclassified from accumulated other comprehensive income (loss)	154		594
Net current-period other comprehensive income (loss)	154		(615)
Accumulated other comprehensive income (loss), ending balance	(13,920)		(14,074)
Proportionate Share of Telesat Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income (loss), beginning balance	238	(15,239)	(15,239)
Other comprehensive income (loss) before reclassification	(3,192)		15,477
Amounts reclassified from accumulated other comprehensive income (loss)
Net current-period other comprehensive income (loss)	(3,192)		15,477
Accumulated other comprehensive income (loss), ending balance	(2,954)		238
Accumulated Other Comprehensive Loss [Member]
Accumulated other comprehensive income (loss), beginning balance	(13,836)	$ (28,698)	(28,698)
Other comprehensive income (loss) before reclassification	(3,192)		14,268
Amounts reclassified from accumulated other comprehensive income (loss)	154		594
Net current-period other comprehensive income (loss)	(3,038)		14,862
Accumulated other comprehensive income (loss), ending balance	$ (16,874)		$ (13,836)