Common Stock Repurchases - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended	11 Months Ended	35 Months Ended
	Apr. 30, 2017	Apr. 30, 2017	Apr. 30, 2017	Apr. 30, 2017	May 26, 2016	Jun. 02, 2014
2016 Repurchase program
Stockholders Equity Note [Line Items]
Repurchase of common stock (in shares)	8,090	8,090	8,090
Repurchase of common stock	$ 600,000	$ 600,000	$ 600,000
Average purchase price of common stock	$ 71.46	$ 71.46	$ 71.46
2016 Repurchase program | Maximum
Stockholders Equity Note [Line Items]
Amount authorized for repurchase of Company's common stock					$ 15,000,000
2014 repurchase program
Stockholders Equity Note [Line Items]
Repurchase of common stock (in shares)	13,578	13,578		380,771
Repurchase of common stock	$ 1,000,000	$ 1,000,000		$ 30,000,000
Average purchase price of common stock	$ 74.08	$ 74.08		$ 78.76
2014 repurchase program | Maximum
Stockholders Equity Note [Line Items]
Amount authorized for repurchase of Company's common stock						$ 30,000,000
Repurchased stock of unused capacity						$ 1,000,000