Accumulated Other Comprehensive Loss (Components of Other Comprehensive Income and Related Tax Effects) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Loss [Abstract]
Amortization of prior service credits and net actuarial loss, Before-Tax Amount	[1]	$ 257	$ 229	$ 770	$ 687
Proportionate share of Telesat other comprehensive income (loss), Before-Tax Amount		(19,255)	2,580	(24,184)	17,522	[2]
Other comprehensive income (loss), Before-Tax Amount		(18,998)	2,809	(23,414)	18,209
Amortization of prior service credits and net actuarial loss, Tax (Provision) Benefit		(90)	(88)	(270)	(261)
Proportionate share of Telesat other comprehensive income (loss), Tax (Provision) Benefit		6,732	(1,008)	8,469	(6,659)
Other comprehensive income, Tax (Provision) Benefit		6,642	(1,096)	8,199	(6,920)
Amortization of prior service credits and net actuarial gain (loss), Net-of-Tax Amount		167	141	500	426
Proportionate share of Telesat other comprehensive income (loss), Net-of-Tax Amount		(12,523)	1,572	(15,715)	10,863
Other comprehensive income (loss), Net-of-Tax Amount		$ (12,356)	$ 1,713	$ (15,215)	11,289
Equity method OCI previously suspended recovered					20,800
Equity method OCI previously suspended recovered, net of tax					$ 13,500

[1] Reclassifications are included in general and administrative expenses.

[2] Includes $20.8 million ($13.5 million, net of tax) share in the equity of Telesat's other comprehensive income that we could not record in 2015 (see Note 5)