Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($)							2 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Aug. 06, 2020	Jun. 16, 2020	Apr. 24, 2020	Apr. 20, 2020	Nov. 22, 2019	Nov. 05, 2019	Aug. 06, 2020	Sep. 10, 2020	Jul. 31, 2020	Jan. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Oct. 31, 2020	Oct. 31, 2019	Jun. 08, 2020
Nature Of Business And Basis Of Presentation [Line Items]
Research and development expenses									$ 1,027,000		$ 1,977,000	$ 3,323,000	$ 12,435,000
Unrestricted cash and cash equivalents									66,300,000			66,300,000			$ 9,400,000
Unrestricted cash and cash equivalents balance excluding amounts funded									$ 50,100,000			50,100,000			9,400,000
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Sale of common stock, net of fees (in shares)									25,144,704	7,938,228	43,997,807
Orion Energy Partners Investment Agent, LLC Credit Facility [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Proceeds from long-term lines of credit												16,200,000			0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Senior Secured Credit Facility [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Long-term line of credit															200,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Initial Funding [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Drew down to fully repay debt outstanding															14,500,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Drew down to fully repay debt outstanding					$ 65,500,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Remainder of Funding [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Line of credit receivable amount															$ 120,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Remainder of Funding [Member] | Maximum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Line of credit receivable amount									$ 120,000,000.0			$ 120,000,000.0
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Fifth Orion Amendment [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Line of credit facility, maximum borrowing capacity																$ 35,000,000
PPP Note [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from promissory note			$ 6,500,000
Period of utilization of amount from promissory notes				168 days
PPP Note [Member] | Minimum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Percentage of payroll to be utilized from proceeds				60.00%
Joint Development Agreement [Member] | Exxon Mobile Research And Engineering Company [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Payment for exclusivity and technology access fee						$ 5,000,000.0
Joint Development Agreement [Member] | Maximum [Member] | Exxon Mobile Research And Engineering Company [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Research and development expenses						45,000,000.0
Milestone-based payments						$ 10,000,000.0
Joint Development Agreement [Member] | Scenario Forecast [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Milestone payments eligible for achievement														$ 5,000,000
At Market Issuance Sales Agreement [Member] | Common Stock [Member] | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Sale of common stock, net of fees (in shares)	3,200,000						28,300,000	72,300,000
Average Sale of Stock Price Per Share	$ 2.51						$ 2.55
Gross Proceeds From Issuance Of Common Stock	$ 8,000,000.0						$ 72,300,000
Payments of Stock Issuance Costs	200,000						2,200,000
Proceeds from Issuance of Common Stock	$ 7,800,000						$ 70,100,000
Common Stock, Reserved for Future Issuance								2,700,000
At Market Issuance Sales Agreement [Member] | Maximum [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Aggregate Offering Price		$ 75,000,000