Revenue Revenue - Sale Information, Percent (Details)	3 Months Ended
	Oct. 31, 2019	Oct. 31, 2018
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	40.80%	44.20%
Domestic
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	36.10%	31.40%
Total United States
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	76.90%	75.60%
International
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	23.10%	24.40%