Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Accumulated other comprehensive income (loss), beginning balance			$ (13,836)
Net current-period other comprehensive income (loss)	$ 179	$ 417	(2,859)	$ 9,576
Accumulated other comprehensive income (loss), ending balance	(16,695)		(16,695)		$ (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)			333		594
Net current-period other comprehensive income (loss)			333		(615)
Accumulated other comprehensive income (loss), ending balance	(13,741)		(13,741)		(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)		(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)			333		594
Net current-period other comprehensive income (loss)			(2,859)		14,862
Accumulated other comprehensive income (loss), ending balance	$ (16,695)		$ (16,695)		$ (13,836)