Computation of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 25, 2015	Apr. 25, 2015	Jan. 24, 2015	Oct. 25, 2014	Jul. 26, 2014	Apr. 26, 2014	Jan. 25, 2014	Oct. 26, 2013	Jul. 25, 2015	Jul. 26, 2014	Jul. 27, 2013
Basic earnings per unit
Net income	$ 33,827	$ 20,258	$ 9,432	$ 20,807	$ 16,489	$ 7,895	$ (3,067)	$ 18,660	$ 84,324	$ 39,978	$ 35,188
Weighted-average number of common shares (in shares)									34,045,481	33,773,158	33,012,595
Basic earnings (loss) per common share (in dollars per share)	$ 1.00	$ 0.59	$ 0.28	$ 0.61	$ 0.49	$ 0.23	$ (0.09)	$ 0.56	$ 2.48	$ 1.18	$ 1.07
Diluted earnings per unit
Weighted-average number of common shares (in shares)									34,045,481	33,773,158	33,012,595
Potential common stock arising from stock options, and unvested restricted share units (in shares)									981,207	1,043,223	769,592
Total shares-diluted (in shares)									35,026,688	34,816,381	33,782,187
Diluted earnings (loss) per common share (in dollars per share)	$ 0.97	$ 0.58	$ 0.27	$ 0.59	$ 0.47	$ 0.23	$ (0.09)	$ 0.54	$ 2.41	$ 1.15	$ 1.04
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)									103,896	586,389	1,204,116