Earnings Per Common Share - Computation (Details) - USD ($)
3 Months Ended 6 Months Ended
Jan. 31, 2016
Jan. 31, 2015
Jan. 31, 2016
Jan. 31, 2015
Numerator for basic and diluted earnings per share:        
Net income $ 15,389,000 $ 11,085,000 $ 29,643,000 $ 22,324,000
Less income allocated to participating securities, basic (126,000) (88,000) (244,000) (218,000)
Net income available to common shareholders, basic 15,263,000 10,997,000 29,399,000 22,106,000
Less income allocated to participating securities, diluted (126,000) (88,000) (244,000) (218,000)
Net income available to common shareholders, diluted $ 15,263,000 $ 10,997,000 $ 29,399,000 $ 22,106,000
Denominator for basic and diluted earnings per share, as adjusted for participating securities:        
Denominator for basic earnings per share - weighted average number of shares outstanding attributable to common stock 41,360,279 41,176,804 41,321,762 41,079,573
Dilutive effect of stock options using the treasury stock method and the average market price for the period (in shares) 44,096 60,043 42,727 75,823
Denominator for diluted earnings per share - weighted average number of shares and common stock equivalents attributable to common stock 41,404,375 41,236,847 41,364,489 41,155,396
Earnings per share attributable to common stock:        
Basic earnings per share (in dollars per share) $ 0.37 $ 0.27 $ 0.71 $ 0.54
Diluted earnings per share (in dollars per share) $ 0.37 $ 0.27 $ 0.71 $ 0.54
Stock options excluded from weighted average dilutive common shares outstanding because their inclusion would have been antidilutive (in shares) 15,000