Stockholder's Investments - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended	12 Months Ended					1 Months Ended	12 Months Ended								1 Months Ended		12 Months Ended
	Sep. 30, 2012	Aug. 31, 2010	Jan. 31, 2008	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2008	Jan. 08, 2008	Aug. 31, 2010 Subsequent Event [Member]	Jul. 31, 2013 Service Based Option [Member]	Jul. 31, 2012 Service Based Option [Member]	Jul. 31, 2011 Service Based Option [Member]	Jul. 31, 2013 Service Based Option [Member] Maximum [Member]	Jul. 31, 2013 Performance Based Options [Member]	Jul. 31, 2013 Restricted Stock [Member] Minimum [Member]	Jul. 31, 2013 Restricted Stock [Member] Maximum [Member]	Jul. 31, 2013 Class A nonvoting common stock [Member]	Dec. 31, 2012 Cliff-Vested Restricted Shares [Member]	Jul. 31, 2013 Cliff-Vested Restricted Shares [Member]	Jul. 31, 2013 Cliff-Vested Restricted Shares [Member] Maximum [Member]	Jul. 31, 2013 Restricted Stock Units (RSUs) [Member] Maximum [Member]	Jul. 31, 2013 Service Based Option [Member]	Jul. 31, 2012 Service Based Option [Member]	Jul. 31, 2011 Service Based Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Noncumulative Cash Dividend				$ 0.02
Amount Entitled To Receive Due To Cumulative Preferred Stock Holders				$ 0.84
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period													3 years		5 years	7 years				3 years	2 years
Expiration period of options										10 years				10 years
Vesting period of service based stock options																						33.33%
Outstanding stock options and restricted shares of Class A Nonvoting Common Stock																	5,150,975
Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Authorized For Future Issuance																	4,359,943
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value				$ 11,086,000	$ 8,016,000	$ 6,822,000
Performance based restricted shares outstanding	10,000	100,000		221,667				210,000											5,000
Weighted average exercise price (USD per share)	$ 30.21	$ 28.35	$ 32.83															$ 32.99				$ 30.58	$ 27.05	$ 29.13
Performance Based Restricted Stock Vested				33,333
Performance Based Restricted Stock Forfeited				55,000
Restricted stock units outstanding				10,000
Shares outstanding, new grants										828,450	1,212,450	1,365,500		0
Weighted average exercise price (USD per share)										$ 30.58	$ 27.91	$ 28.86
Weighted-average fair value of options granted during the period (USD per share)	$ 30.21						$ 32.83		$ 28.35									$ 32.99				$ 9.05	$ 8.42	$ 9.59
The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.				3,311,043	3,503,963	3,316,815
Weighted average exercise price of options exercisable				$ 31.46	$ 29.69	$ 29.83
Proceeds from issuance of common stock				20,324,000	3,864,000	8,193,000
Tax benefit on options exercised				1,964,000	777,000	682,000
Options outstanding, ending balance, aggregate intrinsic value				18,900,000
Options outstanding, exercisable, aggregate intrinsic value					11,577,000
Total intrinsic value of options exercised				$ 10,728,000	$ 3,096,000	$ 5,701,000