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. 26, 2019	Oct. 27, 2018	Jul. 28, 2018	Apr. 28, 2018	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jan. 27, 2018	Jan. 28, 2017	Jan. 26, 2019	Jul. 29, 2017	Jul. 30, 2016
Basic earnings per unit
Net income	$ (12,054)	$ 27,830	$ 29,900	$ 17,231	$ 40,059	$ 28,776	$ 43,708	$ 38,796	$ 23,663	$ 51,050	$ 68,835	$ 74,713	$ 62,907	$ 157,217	$ 128,740
Weighted-average number of common shares (in shares)											31,059,140	31,480,660	31,250,376	31,351,367	32,315,636
Basic earnings per common share (in dollars per share)	$ (0.38)	$ 0.89	$ 0.96	$ 0.55	$ 1.29	$ 0.93	$ 1.41	$ 1.24	$ 0.75	$ 1.62	$ 2.22	$ 2.37	$ 2.01	$ 5.01	$ 3.98
Diluted earnings per unit
Weighted-average number of common shares (in shares)											31,059,140	31,480,660	31,250,376	31,351,367	32,315,636
Potential common stock arising from stock options, and unvested restricted share units (in shares)											778,411		555,993	633,364	800,119
Potential shares of common stock issuable on exercise of convertible senior notes											217,394		183,799	0	0
Total shares-diluted (in shares)											32,054,945	32,180,923	31,990,168	31,984,731	33,115,755
Diluted earnings per common share (in dollars per share)	$ (0.38)	$ 0.87	$ 0.94	$ 0.53	$ 1.24	$ 0.90	$ 1.38	$ 1.22	$ 0.74	$ 1.59	$ 2.15	$ 2.32	$ 1.97	$ 4.92	$ 3.89
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											9,887,191		9,958,448	10,085,298	10,076,982
Stock-based awards
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											93,117		130,779	73,830	65,514
Convertible senior notes
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)											4,788,340		4,821,935	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	5,005,734	5,005,734