Significant accounting policies	9 Months Ended
Significant accounting policies	Sep. 30, 2020
Accounting Policies [Abstract]
Significant accounting policies	Significant accounting policies Basis of presentation These unaudited condensed consolidated financial statements have been prepared in accordance with United States generally accepted accounting principles for interim financial statements and accordingly, do not include all disclosures required for annual financial statements. These statements should be read in conjunction with the Company’s audited consolidated financial statements and notes thereto for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019 (the “2019 Form 10-K”). These unaudited condensed consolidated financial statements reflect, in the opinion of management, all adjustments and reclassifications necessary to fairly present the Company’s financial position as of September 30, 2020, the Company’s results of operations for the three and nine months ended September 30, 2020 and the Company’s cash flows for the nine months ended September 30, 2020. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results for the full year. These unaudited condensed consolidated financial statements follow the same significant accounting policies as those described in the notes to the audited consolidated financial statements of the Company for the year ended December 31, 2019, except as described below under Recent Accounting Pronouncements. Principles of consolidation These unaudited condensed consolidated financial statements include the accounts of the Company and its two wholly-owned subsidiaries, Arbutus Biopharma Inc. (“Arbutus Inc.”) and Arbutus Biopharma US Holdings, Inc. All intercompany transactions and balances have been eliminated in consolidation. Net loss attributable to common shareholders per share The Company follows the two-class method when computing net loss attributable to common shareholders per share as the Company has issued Series A participating convertible preferred shares (the “Preferred Shares”), as further described in note 11, that meet the definition of participating securities. The Preferred Shares entitle the holders to participate in dividends but do not require the holders to participate in losses of the Company. Accordingly, if the Company reports a net loss attributable to holders of the Company’s common shares, net losses are not allocated to holders of the Preferred Shares. Net loss attributable to common shareholders per share is calculated based on the weighted average number of common shares outstanding. The calculation of diluted net loss attributable to common shareholders per share does not differ from the calculation of basic net loss attributable to common shareholders per share, as the effect of the Company’s dilutive potential common shares was anti-dilutive. During the nine months ended September 30, 2020 and 2019, potential common shares of 31.6 million and 28.2 million, respectively, consisting of the “if-converted” number of Preferred Shares and outstanding stock and Employee Stock Purchase Plan (“ESPP”) options, were excluded from the calculation of diluted net loss per common share because their inclusion would be anti-dilutive. Revenue recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers (”ASC 606”), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers under a five-step model: (i) identify contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when or as a performance obligation is satisfied. The Company generates revenue primarily through collaboration agreements and license agreements. Such agreements may require the Company to deliver various rights and/or services, including intellectual property rights or licenses and research and development services. Under such agreements, the Company is generally eligible to receive non-refundable upfront payments, funding for research and development services, milestone payments, and royalties. In contracts where the Company has more than one performance obligation to provide its customer with goods or services, each performance obligation is evaluated to determine whether it is distinct based on whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available and (ii) the good or service is separately identifiable from other promises in the contract. The consideration under the contract is then allocated between the distinct performance obligations based on their respective relative stand-alone selling prices. The estimated stand-alone selling price of each deliverable reflects the Company’s best estimate of what the selling price would be if the deliverable was regularly sold on a stand-alone basis and is determined by reference to market rates for the good or service when sold to others or by using an adjusted market assessment approach if the selling price on a stand-alone basis is not available. The consideration allocated to each distinct performance obligation is recognized as revenue when control is transferred to the customer for the related goods or services. Consideration associated with at-risk substantive performance milestones, including sales-based milestones, is recognized as revenue when it is probable that a significant reversal of the cumulative revenue recognized will not occur. Sales-based royalties received in connection with licenses of intellectual property are subject to a specific exception in the revenue standards, whereby the consideration is not included in the transaction price and recognized in revenue until the customer’s subsequent sales or usages occur. Segment information The Company operates as a single segment. Recent accounting pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial position or results of operations upon adoption. In June 2016, the FASB issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments (ASC 326). The guidance is effective for the Company beginning January 1, 2023 and it changes how entities account for credit losses on financial assets and other instruments that are not measured at fair value through net income, including available-for-sale debt securities. The Company is currently evaluating the impact of the new standard on its consolidated financial statements.