Computation of Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Oct. 29, 2016	Oct. 24, 2015	Jul. 30, 2016	Sep. 15, 2015
Basic earnings per unit
Net income	$ 51,050	$ 30,824
Weighted-average number of common shares (in shares)	31,429,493	32,871,240
Basic earnings per common share (in dollars per share)	$ 1.62	$ 0.94
Diluted earnings per unit
Weighted-average number of common shares (in shares)	31,429,493	32,871,240
Potential common stock arising from stock options, and unvested restricted share units (in shares)	770,794	1,015,507
Total shares-diluted (in shares)	32,200,287	33,886,747
Diluted earnings per common share (in dollars per share)	$ 1.59	$ 0.91
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	10,052,770	10,052,004
Stock-based awards
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)	41,302	40,536
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
Convertible Note Hedge
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt Instrument, Convertible, Conversion Price (per share)				$ 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 (per share)				96.89
Class of Warrant or Right, Exercise Price of Warrants or Rights				$ 130.43