Revenue Revenue - Sale Information, Percent (Details)	3 Months Ended		6 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	100.00%	100.00%	100.00%	100.00%
U.S. government
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	41.50%	45.20%	41.20%	44.70%
Domestic
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	36.60%	32.00%	36.30%	31.70%
Total United States
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	78.10%	77.20%	77.50%	76.40%
International
Concentration Risk [Line Items]
Entity wide revenue percentage by major customer type	21.90%	22.80%	22.50%	23.60%