Organization and Accounting Pronouncements	6 Months Ended
Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Accounting Pronouncements	1. Organization and Accounting Pronouncements Description of Business Equillium, Inc. (the Company) was incorporated in the state of Delaware on March 16, 2017. The Company is a clinical-stage biotechnology company leveraging deep understanding of immunology to develop novel products to treat severe autoimmune and inflammatory disorders with high unmet medical need. From inception through June 30, 2021, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing rights to itolizumab (EQ001), conducting non-clinical research, filing three initial Investigational New Drug applications (INDs), conducting clinical development of the Company’s initial product candidate, itolizumab (EQ001), conducting business development activities, and the general and administrative activities associated with operating a public company. In addition, the Company has a limited operating history, has not generated revenues from its principal operations, and the sales and income potential of its business is unproven. Liquidity and Business Risks As of June 30, 2021, the Company had $97.6 million in cash, cash equivalents and short-term investments. The Company has incurred significant operating losses and negative cash flows from operations. The Company expects to use its cash, cash equivalents, and short-term investments to fund research and development of itolizumab (EQ001) and for working capital and other general corporate purposes. The Company does not expect to generate any revenues from product sales unless and until the Company successfully completes development and obtains regulatory approval of itolizumab (EQ001) or any future product candidate, which is unlikely to happen within the next 12 months, if ever. Accordingly, until such time as the Company can generate significant revenue from sales of its product candidates, if ever, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, and collaboration and license agreements. However, the Company may not be able to secure additional financing or enter into such other arrangements in a timely manner or on favorable terms, if at all. As a result of the COVID-19 pandemic and actions taken to slow its spread, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates and uncertainty about economic stability. There can be no assurance that further deterioration in credit and financial markets and confidence in economic conditions will not occur. If equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult to obtain, more costly and/or more dilutive. The Company’s failure to raise capital or enter into such other arrangements when needed would have a negative impact on the Company’s financial condition and could force the Company to delay, reduce or terminate its research and development programs or other operations, or grant rights to develop and market product candidates that the Company would otherwise prefer to develop and market itself. Management believes that the Company’s cash, cash equivalents and short-term investments as of June 30, 2021 will be sufficient to fund operations for at least the next 12 months from the date this Quarterly Report on Form 10-Q is filed with the Securities and Exchange Commission (SEC). The COVID-19 outbreak in the United States and the rest of the world has caused disruptions to the Company’s business, which has delayed results of the Company’s clinical trials and adversely impacted the Company’s business. The Company cannot predict how legal and regulatory responses to concerns about COVID-19 or other major public health issues will impact the Company’s business, nor can it predict potential adverse impacts related to the availability of capital to fund the Company’s operations. Additionally, the Company’s workforce and outside consultants may also be affected, which could result in an adverse impact on the Company’s ability to conduct business. Any of these factors, alone or in combination with others, could harm the Company’s business, results of operations, financial condition or liquidity. However, the magnitude, timing, and duration of any such potential financial impacts cannot be reasonably estimated at this time. Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the SEC related to a quarterly report on Form 10-Q. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) promulgated by the Financial Accounting Standards Board (FASB). Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The condensed consolidated financial statements reflect all adjustments which, in the opinion of management, are necessary for a fair statement of the results for the periods presented. All such adjustments are of a normal and recurring nature. The operating results presented in these condensed consolidated financial statements are not necessarily indicative of the results that may be expected for any future periods. These condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 24, 2021. Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation. Foreign Currency Translation The Company’s wholly-owned subsidiary in Australia uses their local currency as its functional currency. Assets and liabilities are translated into U.S. dollars at quarter-end exchange rates and revenues and expenses are translated at average exchange rates during the quarter and year-to-date periods. Foreign currency translation adjustments for the reported periods are included in accumulated other comprehensive income in the Company’s condensed consolidated statements of comprehensive loss, and the cumulative effect is included in the stockholders’ equity section of the Company’s condensed consolidated balance sheets. Realized and unrealized gains and losses denominated in foreign currencies are recorded in operating expenses in the Company’s condensed consolidated statements of operations. For the three and six months ended June 30, 2021, net realized and unrealized losses totaled $0.1 million, respectively. For the three months ended June 30, 2020, net realized and unrealized gains totaled $0.3 million. For the six months ended June 30, 2020, net realized and unrealized losses totaled $44,000. Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which amends the FASB ASC 840 and creates Topic 842, Leases. The new topic supersedes Topic 840, Leases, and increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requires disclosures of key information about leasing arrangements. For companies that are not emerging growth companies (EGCs), ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. For EGCs, the ASU was to be effective for fiscal years beginning after December 15, 2019. However, in November 2019, the FASB issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326),Derivatives and Hedging (Topic 815) and Leases (Topic 842), Effective Dates (ASU 2019-10), which included a one-year deferral of the effective date of ASU 2016-02 for certain entities. As a result, the ASU is now effective for EGCs for fiscal years beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. The Company expects to adopt the new standard in the fourth quarter of 2021 using the modified retrospective method, under which the Company will apply Topic 842 to existing and new leases as of January 1, 2021, but prior periods will not be restated and will continue to be reported under Topic 840 guidance in effect during those periods. The Company anticipates that the adoption will not have a material impact on its consolidated statements of operations and consolidated comprehensive loss or its consolidated statements of cash flows but expects to recognize right-of-use assets and liabilities for lease obligations associated with its operating leases. In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments, which will require a reporting entity to use a new forward-looking impairment model for most financial assets that generally will result in the earlier recognition of allowances for losses. The ASU, along with related amendments, revised the measurement of credit losses for financial assets measured at amortized cost from an incurred loss to an expected loss methodology. The ASU affected receivables, debt securities, net investment in leases, and most other financial assets that represent a right to receive cash. The standard and other related subsequently issued ASUs will be effective for the Company for annual periods beginning after December 15, 2022, with early adoption permitted beginning in 2019. The Company is currently evaluating the impact that the adoption of the standard and other related subsequently issued ASUs will have on its consolidated financial statements and accompanying footnotes. Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The amendments in this ASU are effective for the Company on January 1, 2021. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements.

Equillium, Inc. (the Company) was incorporated in the state of Delaware on March 16, 2017. The Company is a clinical-stage biotechnology company leveraging deep understanding of immunology to develop novel products to treat severe autoimmune and inflammatory disorders with high unmet medical need.

From inception through June 30, 2021, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing rights to itolizumab (EQ001), conducting non-clinical research, filing three initial Investigational New Drug applications (INDs), conducting clinical development of the Company’s initial product candidate, itolizumab (EQ001), conducting business development activities, and the general and administrative activities associated with operating a public company. In addition, the Company has a limited operating history, has not generated revenues from its principal operations, and the sales and income potential of its business is unproven.

As of June 30, 2021, the Company had $97.6 million in cash, cash equivalents and short-term investments. The Company has incurred significant operating losses and negative cash flows from operations. The Company expects to use its cash, cash equivalents, and short-term investments to fund research and development of itolizumab (EQ001) and for working capital and other general corporate purposes. The Company does not expect to generate any revenues from product sales unless and until the Company successfully completes development and obtains regulatory approval of itolizumab (EQ001) or any future product candidate, which is unlikely to happen within the next 12 months, if ever. Accordingly, until such time as the Company can generate significant revenue from sales of its product candidates, if ever, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, and collaboration and license agreements. However, the Company may not be able to secure additional financing or enter into such other arrangements in a timely manner or on favorable terms, if at all. As a result of the COVID-19 pandemic and actions taken to slow its spread, the global credit and financial markets have experienced extreme volatility, including diminished liquidity and credit availability, declines in consumer confidence, declines in economic growth, increases in unemployment rates and uncertainty about economic stability. There can be no assurance that further deterioration in credit and financial markets and confidence in economic conditions will not occur. If equity and credit markets deteriorate, it may make any necessary debt or equity financing more difficult to obtain, more costly and/or more dilutive. The Company’s failure to raise capital or enter into such other arrangements when needed would have a negative impact on the Company’s financial condition and could force the Company to delay, reduce or terminate its research and development programs or other operations, or grant rights to develop and market product candidates that the Company would otherwise prefer to develop and market itself. Management believes that the Company’s cash, cash equivalents and short-term investments as of June 30, 2021 will be sufficient to fund operations for at least the next 12 months from the date this Quarterly Report on Form 10-Q is filed with the Securities and Exchange Commission (SEC).

The COVID-19 outbreak in the United States and the rest of the world has caused disruptions to the Company’s business, which has delayed results of the Company’s clinical trials and adversely impacted the Company’s business. The Company cannot predict how legal and regulatory responses to concerns about COVID-19 or other major public health issues will impact the Company’s business, nor can it predict potential adverse impacts related to the availability of capital to fund the Company’s operations. Additionally, the Company’s workforce and outside consultants may also be affected, which could result in an adverse impact on the Company’s ability to conduct business. Any of these factors, alone or in combination with others, could harm the Company’s business, results of operations, financial condition or liquidity. However, the magnitude, timing, and duration of any such potential financial impacts cannot be reasonably estimated at this time.

The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and the rules and regulations of the SEC related to a quarterly report on Form 10-Q. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) promulgated by the Financial Accounting Standards Board (FASB). Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. The condensed consolidated financial statements reflect all adjustments which, in the opinion of management, are necessary for a fair statement of the results for the periods presented. All such adjustments are of a normal and recurring nature. The operating results presented in these condensed consolidated financial statements are not necessarily indicative of the results that may be expected for any future periods. These condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 24, 2021.

The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All intercompany transactions and balances have been eliminated in consolidation.

The Company’s wholly-owned subsidiary in Australia uses their local currency as its functional currency. Assets and liabilities are translated into U.S. dollars at quarter-end exchange rates and revenues and expenses are translated at average exchange rates during the quarter and year-to-date periods. Foreign currency translation adjustments for the reported periods are included in accumulated other comprehensive income in the Company’s condensed consolidated statements of comprehensive loss, and the cumulative effect is included in the stockholders’ equity section of the Company’s condensed consolidated balance sheets. Realized and unrealized gains and losses denominated in foreign currencies are recorded in operating expenses in the Company’s condensed consolidated statements of operations. For the three and six months ended June 30, 2021, net realized and unrealized losses totaled $0.1 million, respectively. For the three months ended June 30, 2020, net realized and unrealized gains totaled $0.3 million. For the six months ended June 30, 2020, net realized and unrealized losses totaled $44,000.

Recent Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which amends the FASB ASC 840 and creates Topic 842, Leases. The new topic supersedes Topic 840, Leases, and increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requires disclosures of key information about leasing arrangements. For companies that are not emerging growth companies (EGCs), ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. For EGCs, the ASU was to be effective for fiscal years beginning after December 15, 2019. However, in November 2019, the FASB issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326),Derivatives and Hedging (Topic 815) and Leases (Topic 842), Effective Dates (ASU 2019-10), which included a one-year deferral of the effective date of ASU 2016-02 for certain entities. As a result, the ASU is now effective for EGCs for fiscal years beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. The Company expects to adopt the new standard in the fourth quarter of 2021 using the modified retrospective method, under which the Company will apply Topic 842 to existing and new leases as of January 1, 2021, but prior periods will not be restated and will continue to be reported under Topic 840 guidance in effect during those periods. The Company anticipates that the adoption will not have a material impact on its consolidated statements of operations and consolidated comprehensive loss or its consolidated statements of cash flows but expects to recognize right-of-use assets and liabilities for lease obligations associated with its operating leases.

In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments, which will require a reporting entity to use a new forward-looking impairment model for most financial assets that generally will result in the earlier recognition of allowances for losses. The ASU, along with related amendments, revised the measurement of credit losses for financial assets measured at amortized cost from an incurred loss to an expected loss methodology. The ASU affected receivables, debt securities, net investment in leases, and most other financial assets that represent a right to receive cash. The standard and other related subsequently issued ASUs will be effective for the Company for annual periods beginning after December 15, 2022, with early adoption permitted beginning in 2019. The Company is currently evaluating the impact that the adoption of the standard and other related subsequently issued ASUs will have on its consolidated financial statements and accompanying footnotes.

Adopted Accounting Pronouncements

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The amendments in this ASU simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. The amendments in this ASU are effective for the Company on January 1, 2021. The adoption of this standard did not have a material impact on the Company's condensed consolidated financial statements.