Earnings (Loss) Per Share Attributable to Common Stockholders (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 16, 2017 vote class	Jul. 31, 2021 USD ($) $ / shares shares	Aug. 01, 2020 USD ($) $ / shares shares	Aug. 03, 2019 USD ($) $ / shares shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of new classes of common stock authorized | class	2
Common stock, conversion ratio	1
Numerator:
Net income (loss)		$ (8,876)	$ (67,117)	$ 36,881
Net income (loss) attributable to common stockholders – basic		(8,876)	(67,117)	36,863
Net income (loss) attributable to common stockholders – diluted		$ (8,876)	$ (67,117)	$ 36,864
Denominator:
Weighted-average shares of common stock - basic (in shares) | shares		105,975,403	102,383,282	100,013,462
Weighted-average shares of common stock - diluted (in shares) | shares		105,975,403	102,383,282	103,653,626
Earnings (loss) per share attributable to common stockholders:
Basic (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.37
Diluted (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.36
Class A common stock
Numerator:
Net income (loss)		$ (5,557)	$ (36,860)	$ 16,604
Less: noncumulative dividends to preferred stockholders		0	0	0
Less: undistributed earnings to participating securities		0	0	(8)
Net income (loss) attributable to common stockholders – basic		(5,557)	(36,860)	16,596
Add: adjustments to undistributed earnings to participating securities		0	0	1
Reallocation of undistributed earnings as a result of conversion of Class B common stock to Class A common stock		0	0	20,267
Reallocation of undistributed earnings to Class B common stock		0	0	0
Net income (loss) attributable to common stockholders – diluted		$ (5,557)	$ (36,860)	$ 36,864
Denominator:
Weighted-average shares of common stock - basic (in shares) | shares		66,351,916	56,228,429	45,027,352
Conversion of Class B to Class A common shares outstanding (in shares) | shares		0	0	54,986,110
Effect of dilutive stock options and restricted stock units (in shares) | shares		0	0	3,640,164
Effect of potentially dilutive preferred stock warrants (in shares) | shares		0	0	0
Weighted-average shares of common stock - diluted (in shares) | shares		66,351,916	56,228,429	103,653,626
Earnings (loss) per share attributable to common stockholders:
Basic (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.37
Diluted (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.36
Class B common stock
Numerator:
Net income (loss)		$ (3,319)	$ (30,257)	$ 20,277
Less: noncumulative dividends to preferred stockholders		0	0	0
Less: undistributed earnings to participating securities		0	0	(10)
Net income (loss) attributable to common stockholders – basic		(3,319)	(30,257)	20,267
Add: adjustments to undistributed earnings to participating securities		0	0	0
Reallocation of undistributed earnings as a result of conversion of Class B common stock to Class A common stock		0	0	0
Reallocation of undistributed earnings to Class B common stock		0	0	302
Net income (loss) attributable to common stockholders – diluted		$ (3,319)	$ (30,257)	$ 20,569
Denominator:
Weighted-average shares of common stock - basic (in shares) | shares		39,623,487	46,154,853	54,986,110
Conversion of Class B to Class A common shares outstanding (in shares) | shares		0	0	0
Effect of dilutive stock options and restricted stock units (in shares) | shares		0	0	2,849,737
Effect of potentially dilutive preferred stock warrants (in shares) | shares		0	0	0
Weighted-average shares of common stock - diluted (in shares) | shares		39,623,487	46,154,853	57,835,847
Earnings (loss) per share attributable to common stockholders:
Basic (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.37
Diluted (in dollars per share) | $ / shares		$ (0.08)	$ (0.66)	$ 0.36
IPO | Class A common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock voting rights per share | vote	1
IPO | Class B common stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock voting rights per share | vote	10