Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Interim Financial Information The accompanying condensed consolidated balance sheet at September 30, 2021, and the condensed consolidated statements of operations and comprehensive loss, statements of convertible preferred stock and changes in stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020 and condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position at September 30, 2021 and the results of its operations for the three and nine months ended September 30, 2021 and 2020 and its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 or for any other subsequent interim period. Restricted Cash Cash accounts with any type of restriction are classified as restricted cash. The Company has restricted cash deposits with a bank, which serve as collateral for a letter of credit issued to the landlord of the Company’s leased Waltham facility for a security deposit. The Company classified this amount as restricted cash in the accompanying condensed consolidated balance sheet at September 30, 2021. There was no restricted cash balance at September 30, 2020. Cloud Computing Arrangements The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as the implementation costs incurred to develop or obtain software business applications used in the normal course of business, are capitalized in accordance with ASC 350. Capitalization ceases at the point the software is substantially complete and ready for its intended use, and after all substantial testing is completed. Amortization is recorded on a straight-line basis over the expected useful life of three years of the internal-use software cost in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement. No amortization expense associated with the Company's cloud computing arrangements has been recognized during the three and nine months ended September 30, 2021 and 2020. Functional Currency As a result of certain intercompany transactions in September 2021, the Company has determined that the functional currency for AlloVir International and AlloVir Italia is the U.S. Dollar (“USD”). Prior to this determination, the functional currency of AlloVir International was the Euro; however, due to the immateriality of the transactions that occurred at AlloVir International and AlloVir Italia previously, the impact of the determination for the transition from Euro to USD is not material and is not considered a change in accounting principle for reporting purposes. Reporting currency has been and remains the USD. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with certain new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Since December 31, 2020, there have been no new accounting pronouncements adopted by the Company or issued by FASB that are applicable to the Company, except as noted below. Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12 – Income Taxes (Topic 740) (“ASU 2019-12”), which removes certain exceptions from the guidance and simplifies the accounting for income taxes in certain areas. The Company adopted ASU 2019-12 on January 1, 2021. There was no material impact to the Company’s consolidated financial statements as a result of adopting this new standard. Recently Issued Accounting Pronouncements Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on loans and other financial instruments. ASU 2016-13 is effective for the Company’s fiscal year beginning after December 15, 2022 and subsequent interim periods. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Interim Financial Information

The accompanying condensed consolidated balance sheet at September 30, 2021, and the condensed consolidated statements of operations and comprehensive loss, statements of convertible preferred stock and changes in stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020 and condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. The condensed consolidated interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for the fair presentation of the Company’s financial position at September 30, 2021 and the results of its operations for the three and nine months ended September 30, 2021 and 2020 and its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021 or for any other subsequent interim period.

Restricted Cash

Cash accounts with any type of restriction are classified as restricted cash. The Company has restricted cash deposits with a bank, which serve as collateral for a letter of credit issued to the landlord of the Company’s leased Waltham facility for a security deposit. The Company classified this amount as restricted cash in the accompanying condensed consolidated balance sheet at September 30, 2021. There was no restricted cash balance at September 30, 2020.

Cloud Computing Arrangements

The Company capitalizes certain implementation costs for internal-use software incurred in a cloud computing agreement that is a service contract. Eligible costs associated with cloud computing arrangements, such as the implementation costs incurred to develop or obtain software business applications used in the normal course of business, are capitalized in accordance with ASC 350. Capitalization ceases at the point the software is substantially complete and ready for its intended use, and after all substantial testing is completed. Amortization is recorded on a straight-line basis over the expected useful life of three years of the internal-use software cost in the same line item in the statement of operations and comprehensive loss as the expense for fees for the associated cloud computing arrangement. No amortization expense associated with the Company's cloud computing arrangements has been recognized during the three and nine months ended September 30, 2021 and 2020.

Functional Currency

As a result of certain intercompany transactions in September 2021, the Company has determined that the functional currency for AlloVir International and AlloVir Italia is the U.S. Dollar (“USD”). Prior to this determination, the functional currency of AlloVir International was the Euro; however, due to the immateriality of the transactions that occurred at AlloVir International and AlloVir Italia previously, the impact of the determination for the transition from Euro to USD is not material and is not considered a change in accounting principle for reporting purposes. Reporting currency has been and remains the USD.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with certain new or revised accounting standards pursuant to Section 107(b) of the JOBS Act.

Since December 31, 2020, there have been no new accounting pronouncements adopted by the Company or issued by FASB that are applicable to the Company, except as noted below.

Recently Adopted Accounting Pronouncements

In December 2019, the FASB issued ASU 2019-12 – Income Taxes (Topic 740) (“ASU 2019-12”), which removes certain exceptions from the guidance and simplifies the accounting for income taxes in certain areas. The Company adopted ASU 2019-12 on January 1, 2021. There was no material impact to the Company’s consolidated financial statements as a result of adopting this new standard.

Recently Issued Accounting Pronouncements Not Yet Adopted

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 significantly changes the impairment model for most financial assets and certain other instruments. ASU 2016-13 will require immediate recognition of estimated credit losses expected to occur over the remaining life of many financial assets, which will generally result in earlier recognition of allowances for credit losses on loans and other financial instruments. ASU 2016-13 is effective for the Company’s fiscal year beginning after December 15, 2022 and subsequent interim periods. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements and related disclosures.