Investments in Affiliates (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended				3 Months Ended			6 Months Ended	9 Months Ended
	Apr. 30, 2018	Mar. 31, 2018	Feb. 28, 2017	Jan. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Investments in and Advances to Affiliates [Line Items]
Distribution received from affiliate										$ 242,735
Equity in net income (loss) of affiliates					$ 55,095	$ 43,372			$ 56,734	183,086
Cumulative effect adjustment attributable to investment in Telesat, tax expense (benefit)									(5,900)
Cumulative effect adjustment attributable to investment in Telesat, net of tax									(22,107)
Investments in affiliates					$ 84,363				$ 84,363		$ 53,430
Telesat Canada [Member]
Investments in and Advances to Affiliates [Line Items]
Economic interest in affiliate					62.70%				62.70%		62.70%
Voting interest in affiliate					32.60%				32.60%		32.60%
Distribution received from affiliate							$ 242,700
Equity method investment, share of equity in net income (loss) of investee						82,400
Equity in net income (loss) of affiliates					$ 55,095	43,372			$ 56,734	$ 183,086
Equity method investment, excess cash distribution recognized as equity income								$ 39,000
Investments in affiliates					84,363				84,363		$ 53,430
Equity method investment, excess equity income previously recognized recovered						$ 39,000
Equity method investment, share of equity in other comprehensive income of investee									2,200
Consulting fees payable in cash									5,000
Telesat Canada [Member] | Adjustments for New Accounting Pronouncement [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investment, cumulative effect adjustment on retained earnings									(44,600)
Cumulative effect adjustment attributable to investment in Telesat, tax expense (benefit)									(5,900)
Cumulative effect adjustment attributable to investment in Telesat, net of tax									(22,100)
Investments in affiliates					$ (28,000)				$ (28,000)
Telesat Canada [Member] | Term Loan B - U.S. Facility [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investment, applicable margin on senior credit facility	2.50%		3.00%	3.75%
Equity method investment, debt repayment		$ 50,000
Telesat Canada [Member] | Equity Method Investment Senior Secured Credit Facility [Member]
Investments in and Advances to Affiliates [Line Items]
Minimum total leverage ratio					4.50				4.50
Actual Total Leverage Ratio to incur debt and make payments					4.53				4.53
XTAR, LLC [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in affiliates					$ 0				$ 0		$ 0
Percentage of ownership interest					56.00%				56.00%