Share-based Compensation Expense - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended				12 Months Ended					12 Months Ended		12 Months Ended				12 Months Ended		12 Months Ended			12 Months Ended							12 Months Ended		12 Months Ended							1 Months Ended					12 Months Ended				12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2007 CompensationPlan	Jul. 31, 2012 Total Shareholders Return Year	Jul. 31, 2011 Total Shareholders Return Year	Jul. 31, 2010 Total Shareholders Return Year	Jan. 23, 2012 Stock Incentive Plan 2009	Jan. 29, 2010 Stock Incentive Plan 2009	Jul. 31, 2006 Non-Employee Director Stock Option Plan CompensationPlan	Jul. 31, 2012 Non-Employee Director Stock Option Plan Lapsed Time CompensationPlan	Jul. 31, 2006 Non-Employee Director Stock Option Plan Maximum	Jul. 31, 2006 Non-Employee Director Stock Option Plan Minimum	Jul. 31, 2012 Stock Option Plan 2007	Jul. 31, 2012 Stock Option Plan 2007 Minimum	Jul. 31, 2012 Stock Option Plan 2007 Minimum Certain Circumstances	Jul. 31, 2012 2007 Restricted Stock Plan	Jul. 31, 2012 2007 Restricted Stock Plan Certain Circumstances	Jul. 31, 2006 Key Employee Stock Option Plan CompensationPlan	Jul. 31, 2012 Key Employee Stock Option Plan Lapsed Time CompensationPlan	Jul. 31, 2006 Key Employee Stock Option Plan Maximum	Jul. 31, 2006 Key Employee Stock Option Plan Minimum	Jul. 31, 2006 Key Employee Stock Bonus Plan CompensationPlan	Jul. 31, 2012 Directors Plan	Jul. 31, 2011 Directors Plan	Jul. 31, 2010 Directors Plan	Jan. 28, 2008 Directors Plan	Jul. 31, 2012 Employee Stock Purchase Plan	Jul. 31, 2006 Employee Stock Purchase Plan CompensationPlan	Jul. 31, 2012 Stock Option and Restricted Stock Bonus Plans	Jul. 31, 2012 Stock Options		Jul. 31, 2011 Stock Options		Jul. 31, 2010 Stock Options		Jan. 29, 2010 Stock Options Stock Incentive Plan 2009	Jan. 29, 2010 Stock Options Stock Incentive Plan 2009 Maximum	Jan. 29, 2010 Stock Appreciation Rights (SARs) Stock Incentive Plan 2009	Jan. 29, 2010 Stock Appreciation Rights (SARs) Stock Incentive Plan 2009 Maximum	Jul. 31, 2006 Nonqualified Stock Options Non-Employee Director Stock Option Plan	Jul. 31, 2012 Nonqualified Stock Options Stock Option Plan 2007 Maximum	Jul. 31, 2012 Incentive Stock Option Stock Option Plan 2007 Maximum	Jul. 31, 2012 Performance Based Restricted Share Awards	Jul. 31, 2011 Performance Based Restricted Share Awards	Jul. 31, 2012 Performance Based Restricted Share Awards Maximum	Jul. 31, 2012 Performance Based Restricted Share Awards Minimum	Jul. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units	Jul. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units Earnings Per Share	Jul. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units Total Shareholders Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized to be granted								2,200,000	1,600,000					250,000			500,000										100,000
Common stock, par value	$ 0.05	$ 0.05							$ 0.05					$ 0.05			$ 0.05										$ 0.05
Percentage in which the exercise price is less than that of the fair market value of the common stock on the date of grant																						100.00%															100.00%		100.00%			100.00%	110.00%
Expected options maximum term																															5 years 3 months 26 days	[1]	4 years 8 months 27 days	[1]	4 years 10 months 2 days	[1]		10 years		10 years
Total common stock shares granted																								37,107	3,492	2,325
Annual share retainer value																								$ 70	$ 55	$ 35
Total number of deferred stock units outstanding	28,981	25,419
Number of compensation plans				2						2	1								2	1			2						1
Percentage for voting power															10.00%
Vesting period												10 years	1 year			1 year		1 year			6 years	2 years	4 years																			10 years	5 years
Percentage of awards that vest on the second anniversaries of the date of grant														25.00%
Percentage of awards that vest on the third anniversaries of the date of grant														25.00%
Percentage of awards that vest on the fourth anniversaries of the date of grant														25.00%
Percentage of awards that vest on the fifth anniversaries of the date of grant														25.00%
Expiration period																					7 years
Exercise period										3 years
Percentage of the fair market value of the common stock at the dated of grant																																									100.00%
Time period in which participants may not dispose or otherwise transfer stock granted																							3 years
Restricted stock awards outstanding																																												451,450	447,244			451,450	250,891	200,559
Share based compensation performance period																																												3 years
Share based compensation target award percentage																																														200.00%	0.00%
Share based compensation expense, service period					2.7	2.7	2.7
Weighted average grant date fair value of awards granted					$ 97.31	$ 54.27	$ 47.47
Discount of market value																												85.00%
Voluntary payroll deduction period																												6 months
Maximum outstanding value for each employee for options granted																												25
Shares reserved for grant under the stock option, bonus, and purchase plans	989,093
Weighted average fair value of stock options granted	$ 16.71	$ 15.42	$ 15.39
Intrinsic value of options exercised	489	195	80
Cash received from exercise of options	1,891	1,122	693
Total fair value of restricted stock grants vested in period	1,867	4,138	1,379
Total unrecognized compensation cost related to non-vested share-based compensation arrangements																														12,751
Total unrecognized compensation cost related to non-vested share-based compensation arrangements, weighted average period																														1 year 8 months 19 days
Tax benefit realized for tax deduction from option exercises	$ 26	$ 49	$ 28

[1] The option life was determined by estimating the expected option life, using historical data.