Losses Due to Repurchases under Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2014	Jan. 31, 2013
Loss Contingencies [Line Items]
Cost of units repurchased	$ 326	$ 1,526	$ 449	$ 2,128
Realization of units resold	289	1,264	390	1,769
Losses due to repurchase	$ 37	$ 262	$ 59	$ 359