Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Loss Contingencies [Line Items]
Cost of units repurchased	$ 2,881	$ 5,876	$ 10,001
Realization of units resold	2,521	5,023	8,665
Losses due to repurchase	$ 360	$ 853	$ 1,336