Accounts Receivable (Details) (USD $)	Apr. 30, 2012	Jul. 31, 2011
Total accounts receivable	$ 74,149,000	$ 72,021,000
Less: Allowance for doubtful accounts	1,140,000	1,220,000
Accounts receivable, net	73,009,000	70,801,000
Unbilled receivables on contracts-in-progress due from U.S. government and its agencies	2,942,000	4,487,000
Retainage included in unbilled receivables	13,000	28,000
Billed Receivables [Member] | Non-United States Government Customer [Member]
Total accounts receivable	34,429,000	38,245,000
Billed Receivables [Member] | U.S. Government and Its Agencies [Member]
Total accounts receivable	33,533,000	22,075,000
Unbilled Receivables on Contracts-In-Progress [Member]
Total accounts receivable	$ 6,187,000	$ 11,701,000