Revenue Revenue - Sale Information, Percent (Details)	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	100.00%	100.00%
U.S. government
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	44.20%	32.40%
Domestic
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	31.40%	44.30%
Total United States
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	75.60%	76.70%
International
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	24.40%	23.30%