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Stockholders' Equity and Warrant Liabilities - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions |  |  |  |  |  |  |  | 2 Months Ended | 3 Months Ended | 6 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 11, 2021 | Dec. 07, 2020 | Dec. 04, 2020 | Jan. 08, 2020 | Nov. 22, 2019 | Oct. 31, 2019 | May 03, 2017 | Jul. 31, 2021 | Jul. 31, 2021 | Apr. 30, 2021 | Jan. 31, 2021 | Jul. 31, 2020 | Jan. 31, 2020 | Apr. 30, 2021 | Jul. 31, 2020 | Apr. 08, 2021 | Apr. 07, 2021 | Oct. 31, 2020
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of incremental common stock shares approved |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 162,500,000 |  |
Common stock, shares authorized |  |  |  |  |  |  |  | 500,000,000 | 500,000,000 |  |  |  |  |  |  | 500,000,000 | 337,500,000 | 337,500,000
Sale of stock, price per share |  |  | $ 7.95 | $ 2.29 |  |  |  |  |  |  |  | $ 2.23 | $ 1.59 |  | $ 2.23 |  |  |
Class of warrants or rights issued |  |  |  |  |  |  |  |  |  |  |  |  | 9,396,320 |  |  |  |  |
Class of warrants or rights exercised |  |  |  |  |  |  |  |  |  |  |  |  | 12,000,000 |  |  |  |  |
Expected volatility |  | 117.02% |  | 103.70% |  |  |  |  |  |  |  |  | 104.90% |  | 111.97% |  |  |
Risk-free interest rate |  | 0.70% |  | 1.81% |  |  |  |  |  |  |  |  | 1.45% |  | 0.39% |  |  |
Class of warrants or rights charge |  |  |  | $ 23.7 |  |  |  |  |  |  | $ 16.0 | $ 1.7 | $ 10.5 |  |  |  |  |
Reclassification of estimated fair value of warrant liability to additional paid in capital |  | $ 21.2 |  | $ 26.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period shares new issues |  |  |  |  |  |  |  |  | 43,978,999 |  | 25,000,000 | 25,144,704 | 7,938,228 |  |  |  |  |
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights exercised |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Exercise Price 0.242 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  | $ 0.242 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  | 2,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued value |  | $ 0.6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Initial Funding Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  |  |  |  |  | 6,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  | $ 0.310 |  |  |  |  |  |  |  |  |  |  |  |
Drew down to fully repay debt outstanding |  |  |  |  |  | $ 14.5 |  |  |  |  |  |  |  |  |  |  |  |
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  |  |  |  | 14,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Drew down to fully repay debt outstanding |  |  |  |  | $ 65.5 |  |  |  |  |  |  |  |  |  |  |  |  |
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding Warrants [Member] | Exercise Price 0.242 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  |  |  |  | 8,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  | $ 0.242 |  |  |  |  |  |  |  |  |  |  |  |  |
Orion Energy Partners Investment Agent, LLC Credit Facility [Member] | Second Funding Warrants [Member] | Exercise Price 0.620 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  |  |  |  | 6,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  | $ 0.62 |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued to underwriters |  |  | 19,822,219 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares issued in transaction |  |  | 14,696,320 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of stock, price per share |  |  | $ 6.50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period shares new issues |  |  | 25,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issuance, net of fees |  |  | $ 162.5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting discounts and commissions |  |  | $ 0.2275 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  | $ 156.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwriting Agreement [Member] | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Option to purchase additional common stock shares |  |  | 5,177,781 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
At Market Issuance Sales Agreement [Member] | Jefferies LLC [Member] | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period shares new issues |  |  |  |  |  |  |  | 44,000,000.0 |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  | $ 369.0 |  |  |  |  |  |  |  |  |  |
Aggregate Offering Price | $ 500.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage Of Sales Commission | 2.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Average Sale Of Stock Price Per Share |  |  |  |  |  |  |  | $ 8.56 | $ 8.56 |  |  |  |  |  |  |  |  |
Gross Proceeds From Issuance Of Common Stock |  |  |  |  |  |  |  | $ 376.6 |  |  |  |  |  |  |  |  |  |
Payments of commissions and offering expenses | $ 7.6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale agreement, common stock, value, available for issuance |  |  |  |  |  |  |  | $ 123.4 | $ 123.4 |  |  |  |  |  |  |  |  |
At Market Issuance Sales Agreement [Member] | Maximum | Jefferies LLC [Member] | Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate Offering Price | $ 500.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Underwritten Public Offering [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock issued during period shares new issues |  |  |  |  |  |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Underwritten Public Offering [Member] | May 2017 Offering - Series C Warrants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights issued |  |  |  |  |  |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  |  |  | $ 19.20 |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights exercised |  |  |  |  |  |  |  | 0 | 0 |  |  |  |  |  |  |  |  |
Class of warrant or right term |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |
Underwritten Public Offering [Member] | Common Stock | May 2017 Offering - Series C Warrants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stockholders' Equity Note |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of warrants or rights exercised |  |  |  |  |  |  |  |  |  | 14,026 |  |  |  | 14,026 |  |  |  |
Proceeds from warrant exercises |  |  |  |  |  |  |  |  |  | $ 0.3 |  |  |  | $ 0.3 |  |  |  |

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