Revenue - Disaggregation of Revenues (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 170,448,000	$ 147,854,000	$ 495,425,000	$ 403,154,000
Point in time
Disaggregation of Revenue [Line Items]
Revenues	88,013,000		269,795,000
Over time
Disaggregation of Revenue [Line Items]
Revenues	82,435,000		225,630,000
Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	145,576,000		428,062,000
Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	24,872,000		67,363,000
U.S. government
Disaggregation of Revenue [Line Items]
Revenues	66,362,000		211,706,000
Domestic
Disaggregation of Revenue [Line Items]
Revenues	59,123,000		162,088,000
Total United States
Disaggregation of Revenue [Line Items]
Revenues	125,485,000		373,794,000
International
Disaggregation of Revenue [Line Items]
Revenues	44,963,000		121,631,000
Commercial Solutions
Disaggregation of Revenue [Line Items]
Revenues	89,600,000		254,308,000
Commercial Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	43,935,000		127,912,000
Commercial Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	45,665,000		126,396,000
Commercial Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	88,125,000		249,982,000
Commercial Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	1,475,000		4,326,000
Commercial Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	17,229,000		52,360,000
Commercial Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	48,248,000		134,178,000
Commercial Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	65,477,000		186,538,000
Commercial Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	24,123,000		67,770,000
Government Solutions
Disaggregation of Revenue [Line Items]
Revenues	80,848,000		241,117,000
Government Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	44,078,000		141,883,000
Government Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	36,770,000		99,234,000
Government Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	57,451,000		178,080,000
Government Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	23,397,000		63,037,000
Government Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	49,133,000		159,346,000
Government Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	10,875,000		27,910,000
Government Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	60,008,000		187,256,000
Government Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	$ 20,840,000		$ 53,861,000