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Fair Value Measurements (Details 1) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2018
Jan. 31, 2017
Fair Value Measurements [Abstract]        
Balance, beginning of period $ 6,300 $ 4,200 $ 6,300 $ 2,000
Purchases 2,200
Balance, end of period 6,300 4,200 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