Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Description of Business	Description of Business Mateon Therapeutics, Inc. (“Mateon” or the “Company”) is a clinical-stage biopharmaceutical company developing drugs for the treatment of orphan oncology indications, with its lead program in acute myeloid leukemia (“AML”). The Company was originally incorporated under the name OXiGENE, Inc. in 1988 in the state of New York and reincorporated in 1992 in the state of Delaware. The Company changed its name to Mateon Therapeutics, Inc. on June 17, 2016.
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with U.S. generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. The financial statements do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In the opinion of management, however, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the three and nine months ended September 30, 2017 are not necessarily indicative of the results that may be expected for any other interim period or for the year ending December 31, 2017. The balance sheet at December 31, 2016 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. For further information, refer to the financial statements and footnotes thereto included in the Annual Report on Form 10-K for the Company for the year ended December 31, 2016.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates.
Cash Equivalents	Cash Equivalents Highly liquid investments with original maturities of three months or less at the date of purchase are considered to be cash equivalents. Cash equivalents are stated at fair value.
Short-term Investments	Short-term Investments All marketable securities have been classified as “available for sale” and are carried at fair value, based upon quoted market prices. The Company considers its available-for-sale portfolio to be available for use in current operations. Accordingly, the Company classifies certain investments as short-term marketable securities, even though the stated maturity date may be one year or more beyond the current balance sheet date. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive income and reported as a separate component of stockholders’ deficit until realized. Realized gains and losses and declines in value judged to be other than temporary, if any, on available-for-sale securities are included in other income (expense), net. The cost of securities sold is based on the specific-identification method.
Going Concern Evaluation	Going Concern Evaluation The Company has experienced net losses every year since inception and, as of September 30, 2017, had an accumulated deficit of approximately $290 million. The Company has no source of revenue and does not expect to receive any product revenue in the near future. If the Company remains in business, the Company expects to incur additional operating losses over the next several years, principally as a result of the Company’s continuing development of its investigational drugs. As of September 30, 2017, the Company had approximately $1.9 million in cash and cash equivalents. Based on the Company’s planned operations, including recent reductions in the Company’s development programs and personnel and assuming the receipt of an anticipated cash refund from one of the Company’s vendors, Management expects Mateon’s existing cash to support operations into February 2018. Prior to this time, the Company will need to secure additional funding or it would be forced to terminate or further curtail operations. Because the Company does not currently have a guaranteed source of capital that will sustain operations past February 2018, Management has determined that there is substantial doubt about the Company’s ability to continue as a going concern. The principal source of the Company’s working capital to date has been the proceeds from the sale of equity. If the Company is unable to access additional funds in the near term, whether through the sale of additional equity or another means, the Company may not be able to continue in business. The Company also may not be able to continue the development of its investigational drugs, and Mateon could be required to delay, scale back or eliminate some or all of its development programs and operations. Any additional equity financing, if available to the Company, may not be available on favorable terms and would most likely be dilutive to current stockholders. Any debt financing, if available, may involve restrictive covenants and also be dilutive to current stockholders. If the Company accesses funds through collaborative or licensing arrangements, it may be required to relinquish rights to some of its technologies or product candidates on terms that are not favorable to the Company. The Company’s ability to access capital when needed is not assured. If access to capital is not achieved in the near term, it will materially harm the Company’s business, financial condition and results of operations.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842),” which requires substantially all leases, including operating leases, to be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability. This ASU is effective for the Company’s interim and annual reporting periods beginning January 1, 2019 and early adoption is permitted. The Company is currently evaluating the impact that the adoption of this ASU will have on its financial statements. In March 2016, the FASB issued ASU No. 2016-09, “Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” which simplified several aspects of the accounting for share-based payments, including immediate recognition of all excess tax benefits and deficiencies in the income statement, changing the threshold to qualify for equity classification up to the employees’ maximum statutory tax rates, allowing an entity-wide accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures as they occur, and clarifying the classification on the statement of cash flows for the excess tax benefit and employee taxes paid when an employer withholds shares for tax-withholding purposes. This ASU became effective for Mateon’s interim and annual reporting periods beginning January 1, 2017, and the adoption of this standard did not have a material impact on the Company’s financial statements. As part of the adoption of this standard, the Company elected to continue estimating the expected option forfeiture rate. In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments,” which addresses several cash flow issues that diversify in practice. The new guidance is effective for fiscal years beginning after December 31, 2017 and for interim periods within those years. The Company currently does not expect the adoption of this ASU to have a material impact on its financial statements.

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.