Accumulated Other Comprehensive Loss (Components of Other Comprehensive Income and Related Tax Effects) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Loss [Abstract]
Amortization of prior service credits and net actuarial loss, Before-Tax Amount	[1]	$ 269	$ 239
Proportionate share of Telesat other comprehensive income (loss), Before-Tax Amount		8,777	(4,929)
Other comprehensive income (loss), Before-Tax Amount		9,046	(4,690)
Amortization of prior service credits and net actuarial loss, Tax (Provision) Benefit		(56)	(85)
Proportionate share of Telesat other comprehensive income (loss), Tax (Provision) Benefit		(1,846)	1,737
Other comprehensive income, Tax (Provision) Benefit		(1,902)	1,652
Amortization of prior service credits and net actuarial gain (loss), Net-of-Tax Amount		213	154
Proportionate share of Telesat other comprehensive income (loss), Net-of-Tax Amount		6,931	(3,192)
Other comprehensive income (loss), Net-of-Tax Amount		$ 7,144	$ (3,038)

[1] Reclassifications are included in other expense.