Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Oct. 31, 2013	Oct. 31, 2012
Loss Contingencies [Line Items]
Cost of units repurchased	$ 123	$ 602
Realization of units resold	101	505
Losses due to repurchase	$ 22	$ 97