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Net Earnings Per Share (Narrative) (Details) - shares
3 Months Ended 6 Months Ended
Oct. 31, 2017
Oct. 31, 2016
Oct. 31, 2017
Oct. 31, 2016
Earnings Per Share [Abstract]        
Shares of its common stock repurchased 194,541 67,400 251,241 139,800
Shares excluded from the calculation of net earnings per share 0 0 0 0