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Fair Value Measurements (Details 1) - USD ($)
$ in Thousands
3 Months Ended
Oct. 31, 2017
Oct. 31, 2016
Fair Value Measurements [Abstract]    
Balance, beginning of period $ 6,300 $ 2,000
Purchases 2,200
Balance, end of period 6,300 4,200
Change in unrealized gains or losses for the period included in earnings for assets held at the end of the period