Revenue - Disaggregation of Revenues (Details) - USD ($)	3 Months Ended		9 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Apr. 30, 2020	Apr. 30, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 135,121,000	$ 170,448,000	$ 467,042,000	$ 495,425,000
Point in time
Disaggregation of Revenue [Line Items]
Revenues	57,923,000	88,013,000	205,117,000	269,795,000
Over time
Disaggregation of Revenue [Line Items]
Revenues	77,198,000	82,435,000	261,925,000	225,630,000
Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	116,632,000	145,576,000	393,995,000	428,062,000
Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	18,489,000	24,872,000	73,047,000	67,363,000
U.S. government
Disaggregation of Revenue [Line Items]
Revenues	41,498,000	66,362,000	178,108,000	211,706,000
Domestic
Disaggregation of Revenue [Line Items]
Revenues	60,813,000	59,123,000	181,444,000	162,088,000
Total United States
Disaggregation of Revenue [Line Items]
Revenues	102,311,000	125,485,000	359,552,000	373,794,000
International
Disaggregation of Revenue [Line Items]
Revenues	32,810,000	44,963,000	107,490,000	121,631,000
Commercial Solutions
Disaggregation of Revenue [Line Items]
Revenues	78,311,000	89,600,000	268,747,000	254,308,000
Commercial Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	25,730,000	43,935,000	106,464,000	127,912,000
Commercial Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	52,581,000	45,665,000	162,283,000	126,396,000
Commercial Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	77,553,000	88,125,000	265,318,000	249,982,000
Commercial Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	758,000	1,475,000	3,429,000	4,326,000
Commercial Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	7,230,000	17,229,000	41,167,000	52,360,000
Commercial Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	51,499,000	48,248,000	158,856,000	134,178,000
Commercial Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	58,729,000	65,477,000	200,023,000	186,538,000
Commercial Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	19,582,000	24,123,000	68,724,000	67,770,000
Government Solutions
Disaggregation of Revenue [Line Items]
Revenues	56,810,000	80,848,000	198,295,000	241,117,000
Government Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	32,193,000	44,078,000	98,653,000	141,883,000
Government Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	24,617,000	36,770,000	99,642,000	99,234,000
Government Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	39,079,000	57,451,000	128,677,000	178,080,000
Government Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	17,731,000	23,397,000	69,618,000	63,037,000
Government Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	34,268,000	49,133,000	136,941,000	159,346,000
Government Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	9,314,000	10,875,000	22,588,000	27,910,000
Government Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	43,582,000	60,008,000	159,529,000	187,256,000
Government Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	$ 13,228,000	$ 20,840,000	$ 38,766,000	$ 53,861,000