Significant Transactions and Adjustments During Fiscal Year 2017 (Details) $ in Thousands	12 Months Ended
	Jul. 31, 2017 USD ($) Nominee	Jul. 31, 2016 USD ($)	Jul. 31, 2015 USD ($)
Reduction in Allowance for Project Disallowances [Abstract]
Reduction of settlement estimate recorded in prior periods	$ 1,132
Reduction of reserves recorded in prior fiscal years	$ 1,132	$ 424	$ 150
Proxy Contest Costs [Abstract]
Number of nominees contesting for Class A directors nomination | Nominee	2
Legal and consulting expenses, net	$ 375	0	0
Recording of Deferred Taxes and Capital in Excess of Par Value Related to Purchases of Noncontrolling Interests in Prior Years [Abstract]
Increase in deferred tax assets	700
Decrease in deferred tax liabilities	(300)
Increase in capital in excess of par value	1,000
Tax Filings of a South American Subsidiary in Prior Years [Abstract]
Current income tax liability	548	2,062	2,615
Interest and penalties expense recorded in administrative and indirect operating expenses	100
Maximum [Member]
Reduction in Allowance for Project Disallowances [Abstract]
Reduction of reserves recorded in prior fiscal years	(100)	(100)	(100)
Tax Filings of a South American Subsidiary in Prior Years [Abstract]
Interest and penalties expense recorded in administrative and indirect operating expenses		$ 100	$ 100
Revenue [Member]
Significant Transactions and Adjustments During Fiscal Year 2017 [Abstract]
Adjustment to statement of operations account	700
Subcontract Costs [Member]
Significant Transactions and Adjustments During Fiscal Year 2017 [Abstract]
Adjustment to statement of operations account	600
South America [Member] | Subsidiaries [Member]
Tax Filings of a South American Subsidiary in Prior Years [Abstract]
Current income tax liability	300
Interest and penalties expense recorded in administrative and indirect operating expenses	100
Contract Receivables, Allowance for Doubtful Accounts and Contract Adjustments [Member]
Significant Transactions and Adjustments During Fiscal Year 2017 [Abstract]
Adjustment to balance sheet account	700
Liabilities to Subcontractors [Member]
Significant Transactions and Adjustments During Fiscal Year 2017 [Abstract]
Adjustment to balance sheet account	$ 600