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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Loss [Abstract]
Amortization of prior service credits and net actuarial loss, Before-Tax Amount	[1]	$ 265	$ 257	$ 797	$ 770
Proportionate share of Telesat other comprehensive income (loss), Before-Tax Amount		(7,115)	(19,255)	2,194	(24,184)
Other comprehensive income (loss), Before-Tax Amount		(6,850)	(18,998)	2,991	(23,414)
Amortization of prior service credits and net actuarial loss, Tax (Provision) Benefit		(56)	(90)	(168)	(270)
Proportionate share of Telesat other comprehensive income (loss), Tax (Provision) Benefit		1,496	6,732	(461)	8,469
Other comprehensive income, Tax (Provision) Benefit		1,440	6,642	(629)	8,199
Amortization of prior service credits and net actuarial gain (loss), Net-of-Tax Amount		209	167	629	500
Proportionate share of Telesat other comprehensive income (loss), Net-of-Tax Amount		(5,619)	(12,523)	1,733	(15,715)
Other comprehensive income (loss), Net-of-Tax Amount		$ (5,410)	$ (12,356)	$ 2,362	$ (15,215)

[1] Reclassifications are included in other expense.