Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
Loss Contingencies [Line Items]
Cost of units repurchased	$ 602	$ 1,700
Realization of units resold	505	1,527
Losses due to repurchase	$ 97	$ 173