Organization and Significant Accounting Policies (Details)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Segments
Number of reportable segments	2
Consolidated revenues | Customer concentration | Agencies of U.S. Government
Concentration of Credit Risk
Concentration risk (as a percent)	70.00%	83.00%	83.00%
Consolidated revenues | Customer concentration | U.S. Army
Concentration of Credit Risk
Concentration risk (as a percent)	43.00%	42.00%	48.00%
Accounts receivable balances | Credit concentration | Agencies of U.S. Government
Concentration of Credit Risk
Concentration risk (as a percent)	39.00%	82.00%
Reportable segment sales | Customer concentration | U.S. Army | UAS
Concentration of Credit Risk
Concentration risk (as a percent)	53.00%	49.00%	56.00%