Computation of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 23, 2016	Jan. 24, 2015	Jan. 23, 2016	Jan. 24, 2015	Sep. 15, 2015	Jul. 25, 2015
Basic earnings per unit
Net income	$ 15,473	$ 9,432	$ 46,297	$ 30,239
Weighted-average number of common shares (in shares)	32,662,942	34,125,829	32,767,088	34,067,983
Basic earnings (loss) per common share (in dollars per share)	$ 0.47	$ 0.28	$ 1.41	$ 0.89
Diluted earnings per unit
Weighted-average number of common shares (in shares)	32,662,942	34,125,829	32,767,088	34,067,983
Potential common stock arising from stock options, and unvested restricted share units (in shares)	857,194	1,001,569	936,350	1,054,547
Total shares-diluted (in shares)	33,520,136	35,127,398	33,703,438	35,122,530
Diluted earnings (loss) per common share (in dollars per share)	$ 0.46	$ 0.27	$ 1.37	$ 0.86
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	10,074,825	283,380	10,072,949	445,254
Stock Compensation Plan [Member]
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	63,357	283,380	61,481	445,254
Convertible Debt Securities [Member]
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	5,005,734	0	5,005,734	0
Note Warrant [Member]
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	5,005,734	0	5,005,734	0
Convertible Note Hedge [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt Instrument, Convertible, Conversion Price					$ 96.89
0.75% Convertible Senior Notes Due 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt, interest rate (in percent)	0.75%		0.75%			0.75%
Debt Instrument, Convertible, Conversion Price					96.89
Class of Warrant or Right, Exercise Price of Warrants or Rights					$ 130.43