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Summary of Significant Accounting Policies - Additional Information (Details) |  | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Sep. 02, 2020 $ / shares | Sep. 30, 2022 USD ($) $ / shares shares | Sep. 30, 2021 USD ($) | Jun. 30, 2021 shares | Sep. 30, 2022 USD ($) Segment $ / shares shares | Sep. 30, 2021 USD ($) | Dec. 31, 2021 USD ($) $ / shares | Sep. 30, 2018 Agreement
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Goodwill or other intangible assets |  | $ 0 |  |  | $ 0 |  |  |
Number of operating agreements of joint venture parties | Agreement |  |  |  |  |  |  |  | 2
Restricted cash |  | 17,500,000 |  |  | 17,500,000 |  | $ 17,500,000 |
Cancellation charges incurred related to purchase of equipment |  | 11,300,000 |  |  | 11,300,000 |  |  |
Impairment of long-lived assets |  | 7,800,000 |  |  | $ 7,806,000 |  |  |
Number of reportable segment | Segment |  |  |  |  | 1 |  |  |
Number of operating segment | Segment |  |  |  |  | 1 |  |  |
Provision for income taxes |  | 0 | $ 0 |  | $ 0 | $ 0 |  |
Current income tax expense (benefit) |  | 0 | 0 |  | 0 | 0 |  |
Deferred income tax expense (benefit) |  | 0 | $ 0 |  | 0 | $ 0 |  |
Accrued Liabilities |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Estimated loss contingency |  | $ 3,500,000 |  |  | $ 3,500,000 |  |  |
Legacy Quantum Scape |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Business combination, effective date of acquisition |  |  |  |  | Nov. 25, 2020 |  |  |
Business combination, date of acquisition agreement |  |  |  |  | Sep. 02, 2020 |  |  |
Business combination exchange ratio | 4.02175014920 |  |  |  |  |  |  |
Public Warrants |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Warrant exercisable number of shares | shares |  | 1 |  |  | 1 |  |  |
Warrants sold | shares |  |  |  |  | 11,499,989 |  |  |
Warrants exercise price per share | $ / shares |  | $ 11.50 |  |  | $ 11.50 |  |  |
Minimum percentage of class A stockholders required for settlement of shares |  | 50.00% |  |  | 50.00% |  |  |
Private Placement Warrants |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Warrants sold | shares |  |  |  |  | 6,650,000 |  |  |
Warrant issued in connection with the closing of business combination | shares |  |  |  |  | 75,000 |  |  |
Class A Common Stock |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Common stock, par value | $ / shares |  | $ 0.0001 |  |  | $ 0.0001 |  | $ 0.0001 |
Number of shares purchased | shares |  |  |  |  | 218,200 |  |  |
Class A Common Stock | Legacy Quantum Scape |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Common stock, par value | $ / shares | $ 0.0001 |  |  |  |  |  |  |
Class A Common Stock | 2020 Equity Employee Stock Purchase Plan |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Common stock reserved for future issuance | shares |  | 11,600,000 |  |  | 11,600,000 |  |  |
Class A Common Stock | 2020 Equity Employee Stock Purchase Plan | Maximum |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Purchase of common stock | shares |  |  |  | 1,000 |  |  |  |
Class B Common Stock |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Common stock, par value | $ / shares |  | $ 0.0001 |  |  | $ 0.0001 |  | $ 0.0001 |
Class B Common Stock | Legacy Quantum Scape |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Common stock, par value | $ / shares | $ 0.0001 |  |  |  |  |  |  |
US Government Money Market Fund and Marketable Securities |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Investment securities |  | $ 231,900,000 |  |  | $ 231,900,000 |  | $ 227,800,000 |
U.S. Government and Agency Securities |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Investment securities |  | 616,500,000 |  |  | $ 616,500,000 |  | $ 722,300,000 |
JVA |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |
Percentage of joint venture holders voting interest |  |  |  |  | 21.60% |  | 19.80% |
Contribution in exchange for equity interests |  | $ 1,700,000 |  |  | $ 1,700,000 |  |  |
Equity interests percentage |  | 50.00% |  |  | 50.00% |  |  |

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