Fair Value of TSR Performance-Based Awards Valuation Assumption (Parenthetical) (Detail)		3 Months Ended		6 Months Ended
		Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Total Shareholders Return Performance-based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected annual dividend yield	[1]	0.00%	0.00%	0.00%	0.00%

[1] Dividends are considered reinvested when calculating TSR. The dividend yield is therefore considered to be 0%.