Stockholders' Equity - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		1 Months Ended		3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Sep. 30, 2012 Class A nonvoting common stock [Member]	Sep. 30, 2011 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]
Remained Shares to repurchase in connection with its repurchase plan						334,940
Number of shares reacquired			2,000,000	2,000,000	188,167
Value of reacquired shares in connection with its repurchase plan	$ 5,121	$ 12,309			$ 5,121
Share repurchased					2,146,773