Organization and Basis of Presentation	12 Months Ended
Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Organization Calithera Biosciences, Inc., or the Company, was incorporated in the State of Delaware on March 9, 2010. The Company is a clinical-stage precision oncology biopharmaceutical company developing targeted therapies to redefine treatment for biomarker-specific patient populations. Driven by a commitment to rigorous science and a passion for improving the lives of people impacted by cancer and other life-threatening diseases, Calithera is advancing a pipeline of investigational, small molecule oncology compounds with a biomarker-driven approach that targets genetic vulnerabilities in cancer cells to deliver new therapies for patients suffering from aggressive hematologic and solid tumor cancers for which there are currently limited treatment options. The Company’s principal operations are based in South San Francisco, California, and it operates in one segment. Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Calithera Biosciences UK Limited and Calithera Biosciences Ireland Limited. All significant intercompany accounts and transactions have been eliminated from the consolidated financial statements. The Company's Ability to Continue as a Going Concern As of December 31, 2021, the Company had cash and cash equivalents of $59.5 million. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of shares of its capital stock and payments from the Company’s collaboration and licensing agreements. As of December 31, 2021, the Company had an accumulated deficit of $491.3 million. During the twelve months ended December 31, 2021, the Company incurred a loss from continuing operations of $115.1 million and used $66.3 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the foreseeable future and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of its existing product candidates, including sapanisertib and mivavotinib, and the achievement of a level of revenues adequate to support its cost structure. In accordance with Accounting Standards Codification, or ASC, 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that these consolidated financial statements are issued on March 31, 2022. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances, including proceeds from our $10.0 million public offering which priced on March 29, 2022 and is expected to close on April 1, 2022, cannot be considered probable at this time because these plans are not entirely within the Company’s control and, with the exception of our recent offering, have not been approved by the board of directors as of the date of these consolidated financial statements. The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these consolidated financial statements are issued on March 31, 2022. Management's plans to alleviate the conditions that raise substantial doubt include the pursuit of additional cash resources through sales of shares of its capital stock, including proceeds from its $10.0 million public offering which priced on March 29, 2022 and is expected to close on April 1, 2022, reduced 2022 spending, and potentially through strategic collaboration or licensing agreements. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these consolidated financial statements. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Organization and Basis of Presentation

12 Months Ended

Dec. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. Organization and Basis of Presentation

Organization

Calithera Biosciences, Inc., or the Company, was incorporated in the State of Delaware on March 9, 2010. The Company is a clinical-stage precision oncology biopharmaceutical company developing targeted therapies to redefine treatment for biomarker-specific patient populations. Driven by a commitment to rigorous science and a passion for improving the lives of people impacted by cancer and other life-threatening diseases, Calithera is advancing a pipeline of investigational, small molecule oncology compounds with a biomarker-driven approach that targets genetic vulnerabilities in cancer cells to deliver new therapies for patients suffering from aggressive hematologic and solid tumor cancers for which there are currently limited treatment options. The Company’s principal operations are based in South San Francisco, California, and it operates in one segment.

Presentation

The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Calithera Biosciences UK Limited and Calithera Biosciences Ireland Limited. All significant intercompany accounts and transactions have been eliminated from the consolidated financial statements.

The Company's Ability to Continue as a Going Concern

As of December 31, 2021, the Company had cash and cash equivalents of $59.5 million. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of shares of its capital stock and payments from the Company’s collaboration and licensing agreements. As of December 31, 2021, the Company had an accumulated deficit of $491.3 million. During the twelve months ended December 31, 2021, the Company incurred a loss from continuing operations of $115.1 million and used $66.3 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the foreseeable future and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of its existing product candidates, including sapanisertib and mivavotinib, and the achievement of a level of revenues adequate to support its cost structure.

In accordance with Accounting Standards Codification, or ASC, 205-40, Going Concern, the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that these consolidated financial statements are issued on March 31, 2022. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances, including proceeds from our $10.0 million public offering which priced on March 29, 2022 and is expected to close on April 1, 2022, cannot be considered probable at this time because these plans are not entirely within the Company’s control and, with the exception of our recent offering, have not been approved by the board of directors as of the date of these consolidated financial statements.

The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these consolidated financial statements are issued on March 31, 2022. Management's plans to alleviate the conditions that raise substantial doubt include the pursuit of additional cash resources through sales of shares of its capital stock, including proceeds from its $10.0 million public offering which priced on March 29, 2022 and is expected to close on April 1, 2022, reduced 2022 spending, and potentially through strategic collaboration or licensing agreements. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these consolidated financial statements.

The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.