Stock Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 35.12
Shares authorized	3,341,296		3,341,296
Shares reserved for future issuance	4,014,866		4,014,866
Share-based compensation expense	$ 2,153	$ 2,238	$ 5,897	$ 5,394
Share-based compensation expense (net of tax)	1,614	$ 1,387	4,423	$ 3,344
Unrecognized compensation cost related to share-based compensation, pre tax	$ 14,492		$ 14,492
Weighted average period remaining			1 year 10 months 24 days
Options Outstanding, Exercisable	1,962,475	2,037,018	1,962,475	2,037,018
Options Outstanding, Exercisable, Weighted Average Exercise Price	$ 26.61	$ 28.67	$ 26.61	$ 28.67
Proceeds from stock options exercised	$ 6,699	$ 5,846	$ 9,948	$ 14,659
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	512	353	895	1,453
Intrinsic value of stock options exercised	2,935	6,719
Fair value of stock options vested	3,004	$ 2,890
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value			5	$ 4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Nonvested	$ 21		$ 21
Service Based Restricted Shares and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value			$ 36.68