Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Stock-based compensation, additional disclosures [Abstract]
Stock-based compensation expense	$ 1.7		$ 1.3	$ 3.5		$ 2.7
Income tax benefit related to stock-based compensation expense	0.6		0.4	1.3		0.9
Intrinsic value of options exercised computed as the market price on the exercise date less the price paid to exercise the options	1.7		0	4.1		0.1
Cash received from exercise of options	1.3		0.1	3.2		0.1
Tax benefit recorded as credits to additional paid-in capital related to stock-based compensation transactions	0.7		0	1.6		0
Shares of common stock available for grant under stock-based incentive plans (in shares)	2,900,000			2,900,000
Aggregate intrinsic value of restricted stock units that are expected to vest	15.8			15.8
Unrecognized compensation expense related to non-vested restricted stock units, expected to be recognized over a weighted-average period of 1.76 years	7.5			7.5
Unrecognized compensation expense, weighted-average period of recognition (in years)				1 year 7 months 10 days
Aggregate intrinsic value of stock options outstanding, all fully vested	$ 0.5			$ 0.5
Restricted Stock Units [Member]
Summary of Restricted Stock Units Activity [Roll Forward]
Outstanding at beginning of period (in shares)				935,633
Granted (in shares)				31,506	[1]
Vested (in shares)				(43,553)
Forfeited (in shares)				(12,644)
Outstanding at end of period (in shares)	910,942			910,942
Weighted Average Measurement Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 14.42
Granted (in dollars per share)				$ 14.36
Vested (in dollars per share)				$ 15.22
Forfeited (in dollars per share)				$ 14.50
Outstanding at end of period (in dollars per share)	$ 14.38			$ 14.38
Stock Options [Member]
Summary of Stock Option activity [Roll Forward]
Outstanding at beginning of period (in shares)				557,954
Exercised (in shares)				(455,379)
Expired (in shares)				(2,575)
Outstanding at end of period (in shares)	100,000	[2]		100,000	[2]
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)				$ 7.84
Exercised (in dollars per share)				$ 6.91
Expired (in dollars per share)				$ 7.16
Outstanding at end of period (in dollars per share)	$ 12.10			$ 12.10
Stock-based compensation, additional disclosures [Abstract]
Weighted average remaining contractual term (in years)				1 year 9 months 4 days

[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.

[2] The weighted average remaining contractual term is 1.76 years.