Losses Due to Repurchases Related to Repurchase Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Loss Contingencies [Line Items]
Cost of units repurchased	$ 189	$ 4,582	$ 1,008	$ 6,227
Realization of units resold	$ 189	3,721	876	5,161
Losses due to repurchase		$ 861	$ 132	$ 1,066