Computation of Earnings Per Common Share - Basic and Diluted Earnings Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Oct. 28, 2017	Oct. 29, 2016
Basic earnings per unit
Net income	$ 28,776	$ 51,050
Weighted-average number of common shares (in shares)	31,061,448	31,429,493
Basic earnings per common share (in dollars per share)	$ 0.93	$ 1.62
Diluted earnings per unit
Weighted-average number of common shares (in shares)	31,061,448	31,429,493
Potential common stock arising from stock options, and unvested restricted share units (in shares)	830,126	770,794
Total shares-diluted (in shares)	31,891,574	32,200,287
Diluted earnings per common share (in dollars per share)	$ 0.90	$ 1.59
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	10,136,542	10,052,770
Stock-based awards
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	125,074	41,302
Convertible senior notes
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	5,005,734	5,005,734
Warrants
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	5,005,734	5,005,734