Losses Due to Repurchases Related to Repurchase Agreements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Cost of units repurchased	$ 4,453	$ 4,650	$ 7,171
Realization of units resold	4,151	3,832	5,906
Losses due to repurchase	$ 302	$ 818	$ 1,265