Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Level 2	Dec. 31, 2012 Level 2
Accounting policy disclosures
Amount of transfers between levels within the fair value hierarchy	$ 0	$ 0
Fair value measurements
Orbital incentive obligations			$ 47.8	$ 30.0