Stockholders' Equity - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended		0 Months Ended		3 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Sep. 07, 2012 Class A nonvoting common stock [Member]	Sep. 12, 2011 Class A nonvoting common stock [Member]	Jan. 31, 2013 Class A nonvoting common stock [Member]	Oct. 31, 2012 Class A nonvoting common stock [Member]	Jul. 31, 2012 Class A nonvoting common stock [Member]
Schedule Of Stockholders Equity [Line Items]
Shares authorized for repurchase			2,000,000	2,000,000
Shares remaining for repurchase					2,146,773		334,940
Number of shares reacquired					0	188,167
Value of reacquired shares in connection with its repurchase plan	$ 5,121	$ 12,309				$ 5,121