Computation of Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jan. 24, 2015	Jan. 25, 2014	Jan. 24, 2015	Jan. 25, 2014
Basic earnings per unit
Net income	$ 9,432	$ (3,067)	$ 30,239	$ 15,593
Weighted-average number of common shares (in shares)	34,125,829	33,836,099	34,067,983	33,629,884
Basic earnings (loss) per common share (in dollars per share)	$ 0.28	$ (0.09)	$ 0.89	$ 0.46
Diluted earnings per unit
Weighted-average number of common shares (in shares)	34,125,829	33,836,099	34,067,983	33,629,884
Potential common stock arising from stock options, and unvested restricted share units (in shares)	1,001,569	0	1,054,547	1,138,061
Total shares-diluted (in shares)	35,127,398	33,836,099	35,122,530	34,767,945
Diluted earnings (loss) per common share (in dollars per share)	$ 0.27	$ (0.09)	$ 0.86	$ 0.45
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	283,380	3,440,300	445,254	753,914