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Losses Due to Repurchases Related to Repurchase Agreements (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jan. 31, 2017
Jan. 31, 2016
Jan. 31, 2017
Jan. 31, 2016
Commitments and Contingencies Disclosure [Abstract]        
Cost of units repurchased $ 1,306 $ 189 $ 2,858 $ 1,008
Realization of units resold 1,118 $ 189 2,662 876
Losses due to repurchase $ 188   $ 196 $ 132