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. 25, 2020	Oct. 26, 2019	Jul. 27, 2019	Apr. 27, 2019	Jan. 26, 2019	Oct. 27, 2018	Jul. 28, 2018	Apr. 28, 2018	Jan. 27, 2018	Jan. 28, 2017	Jan. 25, 2020	Jan. 26, 2019	Jul. 29, 2017
Basic earnings per unit
Net income	$ (11,189)	$ 24,229	$ 29,896	$ 14,279	$ (12,054)	$ 27,830	$ 29,900	$ 17,231	$ 68,835	$ 74,713	$ 57,215	$ 62,907	$ 157,217
Weighted-average number of common shares (in shares)									31,059,140	31,480,660	31,498,474	31,250,376	31,351,367
Basic earnings per common share (in dollars per share)	$ (0.35)	$ 0.77	$ 0.95	$ 0.45	$ (0.38)	$ 0.89	$ 0.96	$ 0.55	$ 2.22	$ 2.37	$ 1.82	$ 2.01	$ 5.01
Diluted earnings per unit
Weighted-average number of common shares (in shares)									31,059,140	31,480,660	31,498,474	31,250,376	31,351,367
Potential common stock arising from stock options, and unvested restricted share units (in shares)									778,411		323,308	555,993	633,364
Potential shares of common stock issuable on exercise of convertible senior notes									217,394		0	183,799	0
Total shares-diluted (in shares)									32,054,945	32,180,923	31,821,782	31,990,168	31,984,731
Diluted earnings per common share (in dollars per share)	$ (0.35)	$ 0.76	$ 0.94	$ 0.45	$ (0.38)	$ 0.87	$ 0.94	$ 0.53	$ 2.15	$ 2.32	$ 1.80	$ 1.97	$ 4.92
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)									9,887,191		9,748,412	9,958,448	10,085,298
Stock-based awards
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)									93,117		253,000	130,779	73,830
Convertible senior notes
Diluted earnings per unit
Anti-dilutive weighted shares excluded from the calculation of earnings per share (in shares)									4,788,340		4,747,706	4,821,935	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		4,747,706	5,005,734	5,005,734