Investments in Affiliates (Narrative) (Details) $ / shares in Units, $ in Thousands, CAD in Millions		3 Months Ended						6 Months Ended			12 Months Ended
	Feb. 01, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 CAD shares	Mar. 31, 2016 USD ($) shares	Mar. 31, 2009 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Investments in and Advances to Affiliates [Line Items]
Equity in net income (loss) of affiliates				$ 43,357				$ 139,714	$ 89,851
Net income (loss)		$ (2,177)		32,552				69,182	63,238
Proportionate share of Telesat other comprehensive income (loss), Before-Tax Amount				494				(4,929)	14,942	[1]
Proportionate share of Telesat other comprehensive income (loss)				259				(3,192)	9,291
Distribution received from affiliate								242,735
Investments in affiliates												$ 107,950
Commitments to provide financial support
Equity method OCI previously suspended recovered									20,800
Telesat Holdings Inc [Member]
Investments in and Advances to Affiliates [Line Items]
Economic interest in affiliates		62.70%						62.70%				62.70%	62.80%
Voting interest in affiliate		32.70%						32.70%				32.70%
Share appreciation rights exercised by Telesat employees | shares					178,642	178,642
Non-voting participating preferred stock issued to Telesat employees | shares					129,400	129,400
Equity method investee, stock options buy back, shares | shares					1,253,477	1,253,477
Equity method investee, stock options buy back, amount | CAD					CAD 24.7
Equity in net income (loss) of affiliates				43,357				$ 139,714	89,851
Distribution received from affiliate			$ 242,700
Distributions declared to shareholders, option holders and certain employees			400,000
Investments in affiliates		$ 0	0					0				$ 107,950
Equity method investment, excess cash distribution recognized as equity income			$ 103,800					39,000
Equity method investment, excess equity income previously recognized recovered		64,800
Profits recognized on affiliate sales eliminated in earlier periods		1,600
Equity method investment unrecognized gain in other comprehensive income		(7,600)
Equity method losses previously suspended recovered						$ 57,900
Equity method OCI previously suspended recovered						$ 20,800
Equity method investment, excess cash distribution recoverable from future equity in investee earnings		$ 46,600						$ 46,600
Indenture maturity date								Nov. 17, 2023
Telesat Holdings Inc [Member] | 6% Senior Notes Due May 2017 [Member]
Investments in and Advances to Affiliates [Line Items]
Interest on notes		6.00%						6.00%
Telesat Holdings Inc [Member] | 6% Senior Notes [Member]
Investments in and Advances to Affiliates [Line Items]
Debt instrument, repurchase date								Nov. 17, 2016
Senior notes issued		$ 0						$ 0
Telesat Holdings Inc [Member] | Senior Notes 8.875% [Member]
Investments in and Advances to Affiliates [Line Items]
Interest on notes		8.875%						8.875%
Indenture maturity date								Nov. 17, 2024
Senior notes issued		$ 500,000						$ 500,000
Telesat Holdings Inc [Member] | Equity Method Investment Term Loan [Member]
Investments in and Advances to Affiliates [Line Items]
Term loan borrowings		2,430,000						2,430,000
Telesat Holdings Inc [Member] | Equity Method Investment Revolving Credit [Member]
Investments in and Advances to Affiliates [Line Items]
Revolving credit borrowings		$ 200,000						$ 200,000
Indenture maturity date								Nov. 17, 2021
Telesat Holdings Inc [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		4.76						4.76
Consulting fees payable in cash								$ 5,000
Telesat Holdings Inc [Member] | Equity Method Investment Senior Secured Facilities Repriced [Member]
Investments in and Advances to Affiliates [Line Items]
Term loan borrowings	$ 2,424,000
Debt instrument amendment date	Feb. 01, 2017
Telesat Holdings Inc [Member] | Transaction, Consulting Agreement [Member]
Investments in and Advances to Affiliates [Line Items]
Transaction payments received during the period								2,400	$ 2,400
Telesat Holdings Inc [Member] | Management [Member]
Investments in and Advances to Affiliates [Line Items]
Equity method investee, stock options buy back, amount | CAD					CAD 18.7
Telesat Holdings Inc [Member] | Restatement Adjustment [Member] | Overstatement [Member]
Investments in and Advances to Affiliates [Line Items]
Equity in net income (loss) of affiliates				5,100
Net income (loss)				$ 3,200
Earnings per share, basic and diluted | $ / shares				$ 0.10
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%
Amended lease obligation, annual												18,200
Lease agreement, past due															$ 32,300
Lease agreement, deferred amount														$ 6,700
Repayment term past due and deferred lease obligation, years							12 years
Deferred lease obligation, annual payment							$ 5,000
Discount rate for prepayment of restructured past due and deferred lease obligation							9.00%
Cumulative payments of restructured past due and deferred lease obligation								$ 29,200
Equity method investment, investee past due liability		$ 30,800						$ 30,800				28,800
XTAR, LLC [Member] | Scenario, Forecast [Member]
Investments in and Advances to Affiliates [Line Items]
Maximum lease obligation, annual											$ 28,000
XTAR, LLC [Member] | Scenario, Plan [Member]
Investments in and Advances to Affiliates [Line Items]
Lease obligation, Annual											26,000	$ 26,000
Amended lease obligation, annual											$ 9,500

[1] 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)