Losses Due to Repurchases Related to Repurchase Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2017	Apr. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Cost of units repurchased	$ 977	$ 1,961	$ 3,835	$ 2,969
Realization of units resold	930	1,524	3,592	2,400
Losses due to repurchase	$ 47	$ 437	$ 243	$ 569