Computation of Earnings Per Common Share - Basic and Diluted Earnings Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended										6 Months Ended		12 Months Ended
	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jul. 30, 2016	Apr. 23, 2016	Jan. 23, 2016	Oct. 24, 2015	Jan. 27, 2018	Jan. 28, 2017	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Basic earnings per unit
Net income	$ 40,059	$ 28,776	$ 43,708	$ 38,796	$ 23,663	$ 51,050	$ 49,360	$ 33,083	$ 15,473	$ 30,824	$ 68,835	$ 74,713	$ 157,217	$ 128,740	$ 84,324
Weighted-average number of common shares (in shares)											31,059,140	31,480,660	31,351,367	32,315,636	34,045,481
Basic earnings per common share (in dollars per share)	$ 1.29	$ 0.93	$ 1.41	$ 1.24	$ 0.75	$ 1.62	$ 1.57	$ 1.02	$ 0.47	$ 0.94	$ 2.22	$ 2.37	$ 5.01	$ 3.98	$ 2.48
Diluted earnings per unit
Weighted-average number of common shares (in shares)											31,059,140	31,480,660	31,351,367	32,315,636	34,045,481
Potential common stock arising from stock options, and unvested restricted share units (in shares)											778,411		633,364	800,119	981,207
Potential shares of common stock issuable on exercise of convertible senior notes											217,394		0	0	0
Total shares-diluted (in shares)											32,054,945	32,180,923	31,984,731	33,115,755	35,026,688
Diluted earnings per common share (in dollars per share)	$ 1.24	$ 0.90	$ 1.38	$ 1.22	$ 0.74	$ 1.59	$ 1.54	$ 1.00	$ 0.46	$ 0.91	$ 2.15	$ 2.32	$ 4.92	$ 3.89	$ 2.41
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											9,887,191		10,085,298	10,076,982	103,896
Stock-based awards
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											93,117		73,830	65,514	103,896
Convertible senior notes
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											4,788,340		5,005,734	5,005,734	0
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	5,005,734	0