Unaudited statements of redeemable preferred stock and stockholders' equity (deficit) (Parenthetical) - USD ($) $ in Thousands		3 Months Ended
Oct. 23, 2020	Oct. 31, 2020	Oct. 31, 2019	Jul. 31, 2019
Statement of Stockholders' Equity [Abstract]
Issuance of common stock, issuance costs	$ 290	$ 290	$ 56	$ 6,084

Amount of decrease in additional paid in capital (APIC) resulting from direct costs associated with issuing stock. Includes, but is not limited to, legal and accounting fees and direct costs associated with stock issues under a shelf registration.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Balance Type:	debit
Period Type:	duration