Summary of Significant Accounting Policies (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Fiscal Year
Number of weeks in an interim quarterly period	13
Concentration risk
Percentage of sales	100.00%
Increase in operating income	$ 93,377	$ 106,973	$ 51,508
Cash Equivalents
Maximum term of original maturity to classify investments as cash equivalents (in months)	3 months
Long-term contracts method
Concentration risk
Percentage of sales	74.00%
Other method
Concentration risk
Percentage of sales	26.00%
Concentration risk by sales | Customer concentration
Concentration risk
Percentage of concentration risk	100.00%	100.00%	100.00%
Concentration risk by sales | Customer concentration | Total U.S. Government customers
Concentration risk
Percentage of concentration risk	67.00%	65.00%	68.00%
Concentration risk by sales | Customer concentration | U.S. Army
Concentration risk
Percentage of concentration risk	29.00%	28.00%	30.00%
Concentration risk by sales | Customer concentration | U.S. Navy
Concentration risk
Percentage of concentration risk	13.00%	12.00%	11.00%
Concentration risk by sales | Customer concentration | NASA
Concentration risk
Percentage of concentration risk	10.00%	10.00%	13.00%
Concentration risk by sales | Customer concentration | U.S. Air Force
Concentration risk
Percentage of concentration risk	6.00%	6.00%	7.00%
Concentration risk by sales | Customer concentration | Other U.S. Government customers
Concentration risk
Percentage of concentration risk	9.00%	9.00%	7.00%
Concentration risk by sales | Customer concentration | Commercial and foreign customers
Concentration risk
Percentage of concentration risk	33.00%	35.00%	32.00%