Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Loss Contingencies [Line Items]
Cost of units repurchased	$ 1,526	$ 108	$ 2,128	$ 1,808
Realization of units resold	1,264	55	1,769	1,582
Losses due to repurchase	$ 262	$ 53	$ 359	$ 226