Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Stock-based compensation, additional disclosures [Abstract]
Stock-based compensation expense	$ 2.4		$ 2.3	$ 6.5		$ 5.8
Income tax benefit related to stock-based compensation expense	0.7		0.8	2.2		2.1
Intrinsic value of options exercised computed as the market price on the exercise date less the price paid to exercise the options	0.2		0	0.4		4.1
Cash received from exercise of options	0.1		0	0.2		3.2
Tax benefit recorded as credits to additional paid-in capital related to stock-based compensation transactions	1.2		0.6	1.4		2.2
Shares of common stock available for grant under stock-based incentive plans (in shares)	1,900,000			1,900,000
Aggregate intrinsic value of restricted stock units that are expected to vest	28.2			28.2
Unrecognized compensation expense related to non-vested restricted stock units, expected to be recognized over a weighted-average period of 1.91 years	21.0			21.0
Aggregate intrinsic value of stock options outstanding, all fully vested	$ 0.7			$ 0.7
Restricted Stock Units [Member]
Summary of Restricted Stock Units Activity [Roll Forward]
Outstanding at beginning of period (in shares)				948,844
Granted (in shares)				538,462	[1]
Exercised (in shares)				0
Vested (in shares)				(461,521)
Forfeited (in shares)				(11,565)
Expired (in shares)				0
Outstanding at end of period (in shares)	1,014,220			1,014,220
Weighted Average Measurement Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 16.55
Granted (in dollars per share)				$ 27.75	[1]
Exercised (in dollars per share)				$ 0
Vested (in dollars per share)				$ 16.29
Forfeited (in dollars per share)				$ 18.92
Expired (in dollars per share)				$ 0
Outstanding at end of period (in dollars per share)	$ 22.59			$ 22.59
Stock-based compensation, additional disclosures [Abstract]
Unrecognized compensation expense, weighted-average period of recognition (in years)				1 year 10 months 28 days
Stock Options [Member]
Summary of Stock Option activity [Roll Forward]
Outstanding at beginning of period (in shares)				75,000
Granted (in shares)				0
Exercised (in shares)				(30,000)
Vested (in shares)				0
Forfeited (in shares)				0
Expired (in shares)				0
Outstanding at end of period (in shares)	45,000	[2]		45,000	[2]
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 12.07
Granted (in dollars per share)				$ 0
Exercised (in dollars per share)				$ 12.09
Vested (in dollars per share)				$ 0
Forfeited (in dollars per share)				$ 0
Expired (in dollars per share)				$ 0
Outstanding at end of period (in dollars per share)	$ 12.05			$ 12.05
Stock-based compensation, additional disclosures [Abstract]
Weighted average remaining contractual term (in years)				0 years 11 months 1 day

[1] The fair value of restricted stock unit grants is determined based on the closing market price of Orbital’s common stock on the date of grant. Such value is recognized as expense over the service period, net of estimated forfeitures, for all but 159,000 of the grants, whose vesting is contingent upon the closing of the Merger. The value of the 159,000 grants will be recognized as expense over one year beginning at the closing date of the Merger.

[2] The weighted average remaining contractual term is 0.92 years.