Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2013	Apr. 30, 2012
Loss Contingencies [Line Items]
Cost of units repurchased	$ 3,650	$ 953	$ 5,778	$ 2,761
Realization of units resold	3,290	863	5,059	2,445
Losses due to repurchase	$ 360	$ 90	$ 719	$ 316