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Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Thousands |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 02, 2025 USD ($) $ / shares shares | Jun. 08, 2025 | Jun. 06, 2025 | Dec. 02, 2024 USD ($) | Oct. 31, 2025 USD ($) $ / shares shares | Sep. 30, 2025 USD ($) $ / shares shares | Sep. 30, 2024 USD ($) | Sep. 30, 2025 USD ($) $ / shares | Sep. 30, 2024 USD ($) | Dec. 31, 2024 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Cash and investments in marketable securities |  |  |  |  |  |  | $ 270,208 |  | $ 270,208 |  | $ 269,095
Aggregate maximum public offering amount |  |  |  |  |  |  |  |  | 300,000 |  |
Accounts receivable, credit loss expense (reversal) |  |  |  |  |  |  | $ 0 | $ 0 | $ 0 | $ 0 |
Reverse stock split, ratio |  |  |  |  |  |  |  | 0.07 |  | 0.07 | 0.066667
Reverse stock split |  |  |  | Reverse Stock Split Amendment, to effect a reverse stock split of Nektar’s Common Stock at a ratio of one-for-fifteen, effective June 8, 2025. |  |  |  |  | one-for-fifteen reverse stock split |  | one-for-fifteen reverse stock split
Asset Purchase Agreement | Asset Acquisition By Ampersand Capital Partners |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of assets |  |  |  |  | $ 64,700 |  |  |  |  |  |
Ownership interest received |  |  |  |  | 20.00% |  |  |  |  |  |
Sales Agreement |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Aggregate maximum public offering amount |  |  |  |  |  |  |  |  | $ 75,000 |  |
Percentage of gross sale of common stock sold through sales agents commission rate |  |  |  |  |  |  |  |  | 3.00% |  |
At-the-Market Offering |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  |  |  | $ 34,489 | $ 0 |
Common Stock |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Reverse stock split, ratio |  |  | 0.07 |  |  |  |  |  |  |  |
Common Stock | 2025 Offering |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sale and issuance of shares | shares |  | 4,893,618 |  |  |  |  |  |  |  |  |
Offering per share price | $ / shares |  | $ 23.5 |  |  |  |  |  |  |  |  |
Net proceeds from issuance of common stock |  | $ 107,200 |  |  |  |  |  |  |  |  |
Common Stock | At-the-Market Offering |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sale and issuance of shares | shares | [1] |  |  |  |  |  | 600,198 |  |  |  |
Offering per share price | $ / shares |  |  |  |  |  |  | $ 59.24 |  | $ 59.24 |  |
Net proceeds from issuance of common stock |  |  |  |  |  |  | $ 34,300 |  |  |  |
Common Stock | At-the-Market Offering | Subsequent Event |  |  |  |  |  |  |  |  |  |  |
Organization And Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sale and issuance of shares | shares |  |  |  |  |  | 673,725 |  |  |  |  |
Offering per share price | $ / shares |  |  |  |  |  | $ 58.55 |  |  |  |  |
Net proceeds from issuance of common stock |  |  |  |  |  | $ 38,300 |  |  |  |  |
[1] | All share amounts have been retrospectively adjusted to reflect a one-for-fifteen reverse stock split (see Note 6).

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