Income Taxes - Reconciliation of Effective Tax Rate to the Statutory Federal Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2021	Aug. 01, 2020	Aug. 03, 2019
Income Tax Disclosure [Abstract]
Tax at federal statutory rate, amount	$ (12,835)	$ (10,022)	$ 6,472
Tax at federal statutory rate, percent	21.00%	21.00%	21.00%
State taxes, net of federal effect, amount	$ (2,417)	$ (4,868)	$ (1,068)
State taxes, net of federal effect, percent	4.00%	10.20%	(3.50%)
Stock-based compensation, amount	$ (34,314)	$ (2,047)	$ (7,114)
Stock-based compensation, percent	56.10%	4.30%	(23.10%)
CARES Act carryback benefit, amount	$ (13,571)	$ (3,070)	$ 0
CARES Act carryback benefit, percent	22.20%	6.40%	0.00%
Change in valuation allowance, amount	$ 21,789	$ 43,153	$ 0
Change in valuation allowance, percent	(35.70%)	(90.40%)	0.00%
Research and development credits, amount	$ (13,582)	$ (6,536)	$ (5,984)
Research and development credits, percent	22.20%	13.70%	(19.40%)
Uncertain tax positions, amount	$ (40)	$ 2,343	$ 2,030
Uncertain tax positions, percent	0.10%	(4.90%)	6.60%
Return to provision, amount	$ 783	$ (777)	$ (1,821)
Return to provision, percent	(1.30%)	1.60%	(5.90%)
Other, amount	$ 1,946	$ 1,219	$ 1,425
Other, percent	(3.10%)	(2.50%)	4.60%
Provision (benefit) for income taxes	$ (52,241)	$ 19,395	$ (6,060)
Effective tax rate, percent	85.50%	(40.60%)	(19.70%)