Debt Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended
	Dec. 31, 2011 Convertible Senior Subordinated Notes [Member]	Dec. 13, 2006 Convertible Senior Subordinated Notes [Member]	Dec. 31, 2011 Credit Facility [Member]	Dec. 31, 2007 Credit Facility [Member]
Debt Instrument [Line Items]
Face amount		$ 143.8
Interest rate (in hundredths)		2.4375%
Maturity date	2027
Unamortized debt discount	3.4
Term of discount amortization period (in years)	7Y
Terms of conversion feature	The convertible notes are convertible into cash, or a combination of cash and common stock at the company's election, based on an initial conversion rate of 40.8513 shares of the company's common stock per $1,000 in principal amount of the convertible notes (equivalent to an initial conversion price of approximately $24.48 per share) only under any of the following circumstances: (1) if, prior to January 13, 2027, the closing sale price of the common stock of Orbital for at least 20 trading days (whether or not consecutive) in the period of 30 consecutive trading days ending on the last trading day of the preceding calendar quarter is greater than 130% of the conversion price per common share in effect on the applicable trading day; (2) if, prior to January 13, 2027, during the 5 consecutive trading-day period following any 5 consecutive trading-day period in which the trading price of the convertible notes was less than 98% of the product of the closing sale price of the company's common stock multiplied by the applicable conversion rate; (3) if the convertible notes have been called for redemption, at any time prior to the close of business on the third business day prior to the redemption date; (4) if the company elects to distribute to all holders of Orbital common stock certain rights entitling them to purchase, for a period expiring within 60 days, the company's common stock at less than the average of the closing sale prices of Orbital common stock for the 10 consecutive trading days immediately preceding the declaration date of such distribution; (5) if the company elects to distribute to all holders of Orbital common stock, assets, debt securities or certain rights to purchase securities of the company, which distribution has a per share value exceeding 10% of the closing sale price of Orbital common stock on the trading day immediately preceding the declaration date of such distribution; or (6) during a specified period, if a "fundamental change" (as such term is defined in the indenture governing the convertible notes) occurs. The conversion rate is subject to adjustments in certain circumstances set forth in the indenture governing the convertible notes. Upon conversion of the convertible notes, the company will deliver in respect of each $1,000 principal amount of notes tendered for conversion (1) an amount in cash ("principal return") equal to the lesser of (a) the principal amount of the converted notes and (b) the conversion value (such value equal to the conversion rate multiplied by the average price of the company's common shares over a 10 consecutive-day trading period) and (2) if the conversion value is greater than the principal return, an amount in cash or common stock, or a combination thereof (at the company's option) with a value equal to the difference between the conversion value and the principal return. At any time on or after January 21, 2014, the convertible notes are subject to redemption at the option of Orbital, in whole or in part, for cash equal to 100% of the principal amount of the convertible notes, plus unpaid interest, if any, accrued to the redemption date. Holders of the convertible notes may require the company to repurchase the convertible notes, in whole or in part, on January 15, 2014, January 15, 2017 or January 15, 2022, for cash equal to 100% of the principal amount of the convertible notes plus unpaid interest, if any, accrued to the redemption date. In addition, holders of the convertible notes may require the company to repurchase the convertible notes, in whole or in part, for cash equal to 100% of the principal amount of the convertible notes, plus unpaid interest, if any, accrued to the redemption date, if a "fundamental change" occurs prior to maturity of the convertible notes.
Term of credit facility (in years)			5Y
Maximum borrowing capacity			300	100
Expiration date of credit facility			June 7, 2016
Capacity for the issuance of standby letters of credit			125
Maximum increase in borrowing capacity			150
Interest rate description			Loans under the Credit Facility bear interest at LIBOR plus an applicable margin ranging from 1.75% to 2.50%, with the applicable margin varying according to the company's total leverage ratio, or, at the election of the company, at a prime base rate plus 0.75% to 1.50%.
Unused capacity, commitment fee description			pay a quarterly commitment fee for the unused portion of the Credit Facility, if any, at a rate ranging from 0.30% to 0.50%.
Letters of credit issued			17.9
Amount available for borrowings			$ 282.1