Revenue - Disaggregation of Revenues (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 161,654,000	$ 164,133,000	$ 331,921,000	$ 324,977,000
Point in time
Disaggregation of Revenue [Line Items]
Revenues	71,686,000	91,213,000	147,194,000	181,781,000
Over time
Disaggregation of Revenue [Line Items]
Revenues	89,968,000	72,920,000	184,727,000	143,196,000
Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	133,969,000	142,584,000	277,363,000	282,485,000
Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	27,685,000	21,549,000	54,558,000	42,492,000
U.S. government
Disaggregation of Revenue [Line Items]
Revenues	67,089,000	74,300,000	136,610,000	145,344,000
Domestic
Disaggregation of Revenue [Line Items]
Revenues	59,236,000	52,454,000	120,631,000	102,965,000
Total United States
Disaggregation of Revenue [Line Items]
Revenues	126,325,000	126,754,000	257,241,000	248,309,000
International
Disaggregation of Revenue [Line Items]
Revenues	35,329,000	37,379,000	74,680,000	76,668,000
Commercial Solutions
Disaggregation of Revenue [Line Items]
Revenues	96,122,000	86,735,000	190,436,000	164,708,000
Commercial Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	43,011,000	46,031,000	80,734,000	83,976,000
Commercial Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	53,111,000	40,704,000	109,702,000	80,732,000
Commercial Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	95,094,000	85,567,000	187,765,000	161,857,000
Commercial Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	1,028,000	1,168,000	2,671,000	2,851,000
Commercial Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	17,189,000	20,911,000	33,937,000	35,131,000
Commercial Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	54,003,000	43,693,000	107,357,000	85,930,000
Commercial Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	71,192,000	64,604,000	141,294,000	121,061,000
Commercial Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	24,930,000	22,131,000	49,142,000	43,647,000
Government Solutions
Disaggregation of Revenue [Line Items]
Revenues	65,532,000	77,398,000	141,485,000	160,269,000
Government Solutions | Point in time
Disaggregation of Revenue [Line Items]
Revenues	28,675,000	45,182,000	66,460,000	97,805,000
Government Solutions | Over time
Disaggregation of Revenue [Line Items]
Revenues	36,857,000	32,216,000	75,025,000	62,464,000
Government Solutions | Firm fixed price
Disaggregation of Revenue [Line Items]
Revenues	38,875,000	57,017,000	89,598,000	120,628,000
Government Solutions | Cost reimbursable
Disaggregation of Revenue [Line Items]
Revenues	26,657,000	20,381,000	51,887,000	39,641,000
Government Solutions | U.S. government
Disaggregation of Revenue [Line Items]
Revenues	49,900,000	53,389,000	102,673,000	110,213,000
Government Solutions | Domestic
Disaggregation of Revenue [Line Items]
Revenues	5,233,000	8,761,000	13,274,000	17,035,000
Government Solutions | Total United States
Disaggregation of Revenue [Line Items]
Revenues	55,133,000	62,150,000	115,947,000	127,248,000
Government Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	$ 10,399,000	$ 15,248,000	$ 25,538,000	$ 33,021,000