Common Stock Repurchases - Additional Information (Detail) - USD ($)	12 Months Ended			14 Months Ended	38 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2017	Jul. 31, 2017	May 26, 2016	Jun. 02, 2014
Stockholders Equity Note [Line Items]
Repurchase of common stock	$ 4,410,000	$ 13,698,000	$ 13,872,000
2014 repurchase program
Stockholders Equity Note [Line Items]
Repurchase of common stock (in shares)	13,578	171,899	176,611		380,771
Repurchase of common stock	$ 1,000,000	$ 13,700,000	$ 13,900,000		$ 30,000,000
Average purchase price of common stock	$ 74.08	$ 79.66	$ 78.51		$ 78.76
2016 Repurchase program
Stockholders Equity Note [Line Items]
Repurchase of common stock (in shares)	47,708			47,708
Repurchase of common stock	$ 3,400,000			$ 3,400,000
Average purchase price of common stock	$ 71.23			$ 71.23
Maximum | 2014 repurchase program
Stockholders Equity Note [Line Items]
Amount authorized for repurchase of Company's common stock							$ 30,000,000
Maximum | 2016 Repurchase program
Stockholders Equity Note [Line Items]
Amount authorized for repurchase of Company's common stock						$ 15,000,000