XML 105 R11.htm IDEA: XBRL DOCUMENT
v3.20.4

Summary of Significant Accounting Policies | 12 Months Ended
--- | ---
Dec. 31, 2020
Accounting Policies [Abstract] |
Summary of Significant Accounting Policies | Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation Our consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (GAAP). Any reference in these notes to applicable guidance is meant to refer to the authoritative accounting principles generally accepted in the United States as found in the Accounting Standard Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). The consolidated financial statements include the Company and its subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates We have made estimates and judgments affecting the amounts reported in our consolidated financial statements and the accompanying notes. On an ongoing basis, we evaluate our estimates, including critical accounting policies or estimates related to revenue recognition, research and development expenses, income tax provisions, stock-based compensation, leases, derivative financial instruments, inventory, and useful lives of long-lived assets. We base our estimates on historical experience and various relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. The actual results that we experience may differ materially from our estimates. Significant estimates relied upon in preparing these financial statements include, among others, those related to fair value of equity awards, revenue recognition, research and development expenses, leases, fair value of financial instruments, useful lives of property and equipment, income taxes, and our valuation allowance on our deferred tax assets. Segment Information We have determined that our chief executive officer is the chief operating decision maker (CODM). The CODM reviews financial information presented on a consolidated basis. Resource allocation decisions are made by the CODM based on consolidated results. There are no segment managers who are held accountable by the CODM for operations, operating results, and planning for levels or components below the consolidated unit level. As such, we have concluded that we operate as one segment. Revenue Recognition On January 1, 2019, we adopted ASC 606 (Revenue from Contracts with Customers) using the modified retrospective transition method applied to those contracts which were not completed as of January 1, 2019. We recognized the cumulative effect of the adoption as an adjustment to the opening balance of accumulated deficit in the current period consolidated balance sheet. Results for reporting periods beginning after January 1, 2019 are presented under ASC 606, while prior period amounts have not been adjusted and continue to be reported in accordance with our historic accounting (ASC 605). ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. To determine the appropriate amount of revenue to be recognized for arrangements that we determine are within the scope of ASC 606, we perform the following five steps (the five-step model): (i) identify the contract(s) with our 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 each performance obligation is satisfied. Our revenue is primarily generated through grants from government-sponsored and private organizations, product sales and collaboration arrangements. Grant Revenue We have contracts with Biomedical Advanced Research and Development Authority (BARDA), a division of the Office of the Assistant Secretary for Preparedness and Response (ASPR) within the U.S. Department of Health and Human Services (HHS); the U.S. government’s Defense Advanced Research Projects Agency (DARPA); the Bill & Melinda Gates Foundation (Gates Foundation) and other government-sponsored and private organizations for research and development related activities that provide for payments for reimbursed costs, which may include overhead and general and administrative costs as well as a related profit margin. We recognize revenue from these contracts as we perform services under these arrangements when the funding is committed. Associated expenses are recognized when incurred as research and development expense. Revenues and related expenses are presented gross in the consolidated statements of operations as we have determined we are the primary obligor under the arrangements relative to the research and development services we perform as lead technical expert. Collaboration Revenue We account for a contract with a customer that is within the scope of ASC 606 using the five-step model. We account for a contract with a customer that is within the scope of ASC 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations; (ii) each party’s rights regarding the goods and/or services to be transferred can be identified; (iii) the payment terms for the goods and/or services to be transferred can be identified; (iv) the arrangement has commercial substance; and (v) collection of substantially all of the consideration to which we will be entitled in exchange for the goods and/or services that will be transferred to the customer is probable. We also determine the term of the contract based on the period in which we and our customer have present and enforceable rights and obligations for purposes of identifying the performance obligations and determining the transaction price. We evaluate contracts that contain multiple promises to determine which promises are distinct. Promises are considered to be distinct and therefore, accounted for as separate performance obligations, provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. Individual goods or services (or bundles of goods and/or services) that meet both criteria for being distinct are accounted for as separate performance obligations. Promises that are not distinct at contract inception are combined and accounted for as a single performance obligation. Options to acquire additional goods and/or services are evaluated to determine if such option provides a material right to the customer that it would not have received without entering into the contract. If so, the option is accounted for as a separate performance obligation. If not, the option is considered a marketing offer which would be accounted for as a separate contract upon the customer’s election. The transaction price is generally comprised of an upfront payment due at contract inception and variable consideration in the form of payments for our services and materials and milestone payments due upon the achievement of specified events. Other payments the Company could be entitled to include tiered royalties earned when customers recognize net sales of licensed products. We measure the transaction price based on the amount of consideration to which we expect to be entitled in exchange for transferring the promised goods and/or services to the customer. We utilize either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which we will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to arrangements that include payments for a development or regulatory milestone payment, we evaluate whether the associated event is considered probable of achievement and estimate the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within our control or the licensee, such as those dependent upon receipt of regulatory approval, are not considered to be probable of achievement until the triggering event occurs. At the end of each reporting period, we re-evaluate the probability of achievement of each milestone and any related constraint, and if necessary, adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, we recognize revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. We generally allocate the transaction price to each performance obligation based on a relative standalone selling price basis. We develop assumptions that require judgment to determine the standalone selling price for each performance obligation in consideration of applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated research and development costs. However, in certain instances, we allocate variable consideration entirely to one or more performance obligation if the terms of the variable consideration relate to the satisfaction of the respective performance obligation and the amount allocated is consistent with the amount we would expect to receive for the satisfaction of the respective performance obligation. We recognize revenue based on the amount of the transaction price that is allocated to each respective performance obligation when or as the performance obligation is satisfied by transferring a promised good or service to the customer. For performance obligations that are satisfied at a point in time, we recognize revenue when control of the goods and/or services is transferred to the customer. For performance obligations that are satisfied over time, we recognize revenue by measuring the progress toward complete satisfaction of the performance obligation using a single method of measuring progress which depicts the performance in transferring control of the associated goods and/or services to the customer. We generally use input methods to measure the progress toward the complete satisfaction of performance obligations satisfied over time. With respect to arrangements containing a license to our intellectual property that is determined to be distinct from the other performance obligations identified in the arrangement, we recognize revenue from amounts allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which we are expected to complete our performance obligations under an arrangement. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. Product Sales Product sales are associated with our COVID-19 vaccine supply agreements with the U.S. Government and international government agencies. These agreements generally do not provide provisions for various forms of variable consideration, such as discounts, rebates or returns. We recognize revenue from product sales, using the five-step model under ASC 606, based on the fixed price per dose according to the contracts when control of the product transfers to the customer and customer acceptance has occurred, unless such acceptance provisions are deemed perfunctory. Cash and Cash Equivalents We consider all highly liquid investments with an original maturity of 90 days or less from the date of purchase to be cash equivalents. Restricted Cash Restricted cash is composed of amounts held on deposit related to our lease arrangements. The funds are maintained in money market accounts and are recorded at fair value. We classify our restricted cash as either current or non-current based on the terms of the underlying lease arrangement. Cash, Cash Equivalents and Restricted Cash shown in the Consolidated Statements of Cash Flows The following table provides a reconciliation of cash, cash equivalents and restricted cash in the consolidated balance sheets that sum to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands):
|  | December 31,
|  | 2020 |  | 2019
Cash and cash equivalents |  | $ | 2,623,850 |  |  | $ | 235,876 |
Restricted cash |  | 1,032 |  |  | 1,032 |
Restricted cash, non-current |  | 11,053 |  |  | 10,791 |
Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows |  | $ | 2,635,935 |  |  | $ | 247,699 |
Investments We invest our excess cash balances in marketable debt securities. We classify our investments in marketable debt securities as available-for-sale. We report available-for-sale investments at fair value at each balance sheet date, and include any unrealized holding gains and losses (the adjustment to fair value) in accumulated other comprehensive gain (loss), a component of stockholders’ equity. Realized gains and losses are determined using the specific-identification method, and are included in other (expense) income, net in our consolidated statements of operations. We classify our available-for-sale marketable securities as current or non-current based on each instrument’s underlying effective maturity date and for which we have the intent and ability to hold the investment for a period of greater than 12 months. Marketable securities with maturities of less than 12 months are classified as current and are included in investments in the consolidated balance sheets. Marketable securities with maturities greater than 12 months for which we have the intent and ability to hold the investment for greater than 12 months are classified as non-current and are included in investments, non-current in the consolidated balance sheets. We evaluate securities for impairment at the end of each reporting period. Impairment is evaluated considering numerous factors, and their relative significance varies depending on the situation. Factors considered include whether a decline in fair value below the amortized cost basis is due to credit-related factors or non-credit-related factors, the financial condition and near-term prospects of the issuer, and our intent and ability to hold the investment to allow for an anticipated recovery in fair value. A credit-related impairment is recognized as an allowance on the balance sheet with a corresponding adjustment to earnings. Any impairment that is not credit- related is recognized in other comprehensive (loss) income, net of applicable taxes. Accounts Receivable and Allowance for Doubtful Accounts We have accounts receivable amounts due from our product sales and related vaccine supply agreements and our grant agreements. We also have accounts receivable amounts due from strategic collaborators as a result of manufacturing and research and development services provided under collaboration arrangements, or milestones achieved, but not yet paid. Amounts payable to us are recorded as accounts receivable when our right to consideration is unconditional. To estimate the allowance for doubtful accounts, we make judgments about the creditworthiness of our customers based on ongoing credit evaluation and historical experience. There was no allowance for doubtful accounts at December 31, 2020, and 2019. There was no bad debt expense for the years ended December 31, 2020, 2019 or 2018. Concentrations of Credit Risk Financial instruments that subject us to significant concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash, marketable securities, and accounts receivable. Our investment portfolio comprises money market funds, marketable debt securities, including U.S. Treasury securities, debt securities of U.S. government agencies and corporate entities and commercial paper. Our cash management and investment policy limits investment instruments to investment-grade securities with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations. Bank accounts in the United States are insured by the Federal Deposit Insurance Corporation (FDIC) up to $250,000. Our primary operating accounts significantly exceed the FDIC limits. Significant Customers Our accounts receivable are generally unsecured and are from customers in different countries. We generated revenue from grants made by government-sponsored and private organizations, product sales to the U.S. Government and international government agencies, and to a lesser extent, strategic alliances in 2020. Historically, we generated revenue primarily from strategic alliances. A significant portion of our revenue to date has been generated from the following entities that accounted for more than 10% of total revenue and accounts receivable for the periods presented:
| Percentage of Revenue Years Ended December 31, |  | Percentage of Accounts Receivable December 31,
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019
Merck | * |  | 61 | % |  | 49 | % |  | * |  | 13 | %
BARDA | 65 | % |  | 13 | % |  | * |  | 22 | % |  | 54 | %
Vertex | * |  | 10 | % |  | * |  | * |  | 17 | %
AstraZeneca | * |  | * |  | 34 | % |  | * |  | *
U.S. Government (excluding BARDA) | 24 | % |  | * |  | * |  | * |  | *
European Commission | * |  | * |  | * |  | 28 | % |  | *
United Kingdom Government | * |  | * |  | * |  | 11 | % |  | *
South Korea Government | * |  | * |  | * |  | 24 | % |  | *
________ * - Represents an amount of less than 10% Derivative Instruments and Hedging Activities We record all derivatives on our consolidated balance sheets at fair value. The accounting for changes in the fair value of a derivative depends on whether the derivative has been designated and qualifies for hedge accounting. Hedge accounting generally provides for the matching of the timing of gain or loss recognition on the hedging instrument with the recognition of the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk in a fair value hedge or the earnings effect of the hedged forecasted transactions in a cash flow hedge. We may enter into derivative contracts that are intended to economically hedge certain risk, even though hedge accounting does not apply or we elect not to apply hedge accounting. Foreign currency gains or losses associated with derivatives that are not designated as hedging instruments for accounting purposes are recorded within other (expense) income, net, in our consolidated statements of operations. Fair Value Measurements Fair value is defined as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities, which are required to be recorded at fair value, we consider the principal or most advantageous market in which we would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions and credit risk. FASB ASC Topic 820, Fair Value Measurement (ASC 820), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from our independent sources. Unobservable inputs are inputs that reflect our assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The following fair value hierarchy is used to classify assets and liabilities based on the observable inputs and unobservable inputs used to value the assets and liabilities: •Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; •Level 2: Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability; or •Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Our cash equivalents and marketable securities are reported at fair value determined using Level 1 and Level 2 inputs (Note 6). The fair value of our foreign currency forward contracts is calculated using Level 2 inputs, which include currency spot rates, forward rates, interest rate curve and credit or non-performance risk (Note 7). We do not have any non-financial assets or liabilities that should be recognized or disclosed at fair value on a recurring basis at December 31, 2020, 2019 and 2018. As of December 31, 2020 and 2019, we maintain letters of credit of $12.1 million and $11.8 million, respectively, related to our lease arrangements, which are secured by money market accounts in accordance with certain of our lease agreements. The amounts are recorded at fair value using Level 1 inputs and included as restricted cash in our consolidated balance sheets. Inventory Inventory is recorded at the lower of cost or net realizable value, with cost determined on a first-in, first-out (FIFO) basis. We periodically review the composition of inventory in order to identify excess, obsolete, slow-moving or otherwise unsaleable items. If unsaleable items are observed and there are no alternate uses for the inventory, we will record a write-down to net realizable value in the period that the decline in value is first recognized through a charge to cost of sales. The determination of whether inventory costs will be realizable requires estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required. Prior to an initial regulatory approval for our investigational medicines, we expense costs relating to raw materials and production of inventory as research and development expense in our consolidated statements of operations, in the period incurred. When we believe regulatory approval and subsequent commercialization of our investigational medicines is probable, and we also expect future economic benefit from the sales of the investigational medicines to be realized, we will then capitalize the costs of production as inventory. Upon the authorization of distribution and use of our COVID-19 vaccine under an EUA in December 2020, we began to capitalize inventory costs associated with our COVID-19 vaccine, as it was determined that inventory costs incurred subsequent to the EUA had a probable future economic benefit. Construction in Progress Construction in progress includes direct costs related to the construction of various property and equipment, including leasehold improvements, and is stated at original cost. Construction in progress includes costs incurred under construction contracts including project management services, engineering services, design services and development, construction services and other construction-related fees and services. Such costs are not depreciated until the asset is completed and placed into service. Once the asset is placed into service, these capitalized costs will be allocated to certain property and equipment categories and will be depreciated over the estimated useful life of the underlying assets. Property and Equipment Property and equipment are stated at cost, net of accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives of property and equipment are described below:
|  | Estimated Useful Life
Laboratory equipment |  | 5 years
Leasehold improvements |  | Lesser of estimated useful life of improvement or remaining life of related lease
Computer equipment and software |  | 3 years
Internally developed software |  | 3 years
Furniture, fixtures and other |  | 5 years
Right of use asset, financing |  | Lease term
Expenditures for maintenance and repairs are charged to expense as incurred. Upon retirement or sale, the cost of the assets disposed of, and the related accumulated depreciation, are removed from the accounts, and any resulting gain or loss is recorded to other (expense) income, net. Impairment of Long-Lived Assets We evaluate our long-lived assets, which consist of property and equipment, to determine if facts and circumstances indicate that the carrying amount of assets may not be recoverable. If such facts and circumstances exist, we assess the recoverability of the long-lived assets by comparing the projected future undiscounted net cash flows associated with the related asset or group of assets over their remaining lives against their respective carrying amounts. If such review indicates that such cash flows are not expected to be sufficient to recover the recorded value of the assets, the assets are written down to their estimated fair values based on the expected discounted future cash flows attributable to the assets or based on appraisals. For the year ended December 31, 2020, we incurred $1.6 million of impairment expenses. We did not record any impairment expenses for the years ended December 31,2019 and 2018. Leases We adopted ASC 842 (Leases) on January 1, 2019 on a modified retrospective basis under which we recognized and measured leases existing at, or entered into after, the beginning of the period of adoption. We elected the optional transition approach of not adjusting our comparative period financial statements for the impacts of adoption. Therefore, we recognized the effects of applying ASC 842 as a cumulative-effect adjustment to accumulated deficit as of January 1, 2019, the effective date of this standard. Leases are classified at their commencement date, which is defined as the date on which the lessor makes the underlying asset available for use by the lessee, as either operating or finance leases based on the economic substance of the agreement. We recognize lease right-of-use assets and related liabilities in our consolidated balance sheets for both operating and finance leases. Lease liabilities are measured at the lease commencement date as the present value of the future lease payments using the interest rate implicit in the lease. If the rate implicit is not readily determinable, we will utilize our incremental borrowing rate as of the lease commencement date. Lease right-of-use assets are measured as the lease liability plus initial direct costs and prepaid lease payments less lease incentives. The lease term is the non-cancelable period of the lease and includes options to extend or terminate the lease when it is reasonably certain that an option will be exercised. We recognize operating lease cost in operating expense in our consolidated statements of operations, inclusive of rent escalation provisions and rent holidays, on a straight-line basis over the respective lease term. For our finance leases, we recognize depreciation expense associated with the leased asset acquired and recognize interest expense related to the portion of the financing in our consolidated statements of operations. Additionally, we recognize tenant improvement allowances as a reduction to rent expense on a straight-line basis over the respective lease term. Cost of Sales Cost of sales includes cost of raw materials, production, transportation, freight and indirect overhead costs associated with our product revenue during the period and third-party royalties on net sales of our product. Cost of sales also includes adjustments for excess and obsolete inventory to the extent management determines that the cost cannot be recovered based on estimates about future demand. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries and benefits, facilities costs, overhead costs, prelaunch inventory costs, contract services, and other outside costs. The value of goods and services received from contract research organizations and contract manufacturing organizations in the reporting period are estimated based on the level of services performed, and progress in the period in cases when we have not received an invoice from the supplier. Equipment or facilities that are acquired or constructed for research and development activities and that have alternative future uses, in research and development projects or otherwise, should be capitalized and depreciated as tangible assets. However, the costs of equipment or facilities that are acquired or constructed and intangibles that are purchased from others for a particular research and development project and that have no alternative future uses and therefore no separate economic values are considered research and development costs and are expensed when incurred. Certain equipment and leased facilities purchased for our COVID-19 vaccine program prior to the EUA from the FDA were deemed to have no alternative use. The related acquisition costs of such equipment and lease facilities of $109.6 million were charged to research and development expense for the year ended December 31, 2020. We did not recognize such expense for the years ended December 31, 2019 or 2018. Patent Costs Costs to secure, defend and maintain patents are expensed as incurred, and are classified as selling, general and administrative expenses due to the uncertainty of future benefits. Stock-Based Compensation We issue stock-based awards to employees and non-employees, generally in the form of stock options and restricted stock units (RSUs). We account for our stock-based compensation awards in accordance with ASC 718, Compensation—Stock Compensation. Most of our stock-based awards have been made to employees. We measure compensation cost for equity awards at their grant-date fair value and recognize compensation expense over the requisite service period, which is generally the vesting period, on a straight-line basis. The grant date fair value of stock options is estimated using the Black-Scholes option pricing model, which requires management to make assumptions with respect to the fair value of our common stock on the grant date, including the expected term of the award, the expected volatility of our stock, calculated based on a period of time generally commensurate with the expected term of the award, risk-free interest rates and expected dividend yields of our stock. Historically, for periods prior to our IPO, the fair value of the shares of common stock and common units underlying our stock-based awards were determined on each grant date by our board of directors based on valuation estimates from management considering our most recently available independent third-party valuation of our common stock. Our board of directors also assessed and considered, with input from management, additional objective and subjective factors that we believed were relevant and which may have changed from the date of the most recent valuation through the grant date. The grant date fair value of RSUs is estimated based on the fair value of our underlying common stock. For performance-based stock awards, we recognize stock-based compensation expense over the requisite service period using the accelerated attribution method when achievement is probable. We classify stock-based compensation expense in our consolidated statement of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified. Income Taxes We use an asset and liability approach to account for income taxes. We recognize deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial reporting and tax bases of assets and liabilities. These differences are measured using the enacted statutory tax rates that are expected to be in effect for the years in which differences are expected to reverse. Valuation allowances are provided when the expected realization of deferred tax assets does not meet a “more likely than not” criterion. We make estimates and judgments about our future taxable income that are based on assumptions that are consistent with our plans and estimates. Should the actual amounts differ from our estimates, the amount of our valuation allowance could be materially impacted. Changes in these estimates may result in significant increases or decreases to our tax provision in a period in which such estimates are changed, which in turn would affect net income or loss. We recognize tax benefits from uncertain tax positions if we believe the position is more likely than not to be sustained on examination by the taxing authorities based on the technical merits of the position. We make adjustments to these reserves when facts and circumstances change, such as the closing of a tax audit or the refinement of an estimate. The provision for income taxes includes the effects of any reserves for tax positions that are not more likely than not to be sustained, as well as the related net interest and penalties. Net Loss per Share Attributable to Common Stockholders We calculate basic net loss per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period, without consideration for common stock equivalents. Upon the closing of our IPO, all outstanding shares of our redeemable convertible preferred stock were converted into common stock. We calculate diluted net loss per share attributable to common stockholders by dividing net loss attributable to common stockholders by the weighted average number of common shares outstanding after giving consideration to the dilutive effect of restricted common stock and stock options that are outstanding during the period. We have generated a net loss in all periods presented, therefore the basic and diluted net loss per share attributable to common stockholders are the same as the inclusion of the potentially dilutive securities would be anti-dilutive. Comprehensive Loss Comprehensive loss includes net loss and other comprehensive income (loss) for the period. Other comprehensive income (loss) mainly consists of unrealized gains and losses on our investments. Total comprehensive income (loss) for all periods presented have been disclosed in the consolidated statements of comprehensive loss. The components of accumulated other comprehensive gain (loss) for the years ended December 31, 2020 and 2019 are as follows (in thousands):
| Unrealized Gain on Available-for-Sale Debt Securities
Accumulated other comprehensive loss, balance at December 31, 2018 | $ | (1,320) |
Other comprehensive income | 3,124 |
Accumulated other comprehensive gain, balance at December 31, 2019 | 1,804 |
Other comprehensive income | 1,200 |
Accumulated other comprehensive gain, balance at December 31, 2020 | $ | 3,004 |
Recently Adopted Accounting Standards In June 2016, the FASB issued ASU No. 2016-13, Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This standard changes how companies account for credit losses for most financial assets and certain other instruments. For trade receivables, loans and held-to-maturity debt securities, companies will be required to recognize an allowance for credit losses rather than reducing the carrying value of the asset. The amendments in this standard should be applied on a modified retrospective basis to all periods presented. We adopted this standard in the first quarter of 2020. Based on the composition of our investment portfolio and investment policy, the adoption of this standard did not have a material impact on our consolidated financial statements and disclosures. In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This standard requires capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). We adopted this standard in the first quarter of 2020 using the prospective method. The adoption of this standard did not have a material impact on our consolidated financial statements and disclosures. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This standard removes certain exceptions for investments, intra-period allocations and interim calculations, and adds guidance to reduce complexity in accounting for income taxes. We early adopted this standard in the second quarter of 2020. The adoption of this standard did not have a material impact on our consolidated financial statements and disclosures. Recently Issued Accounting Standards Not Yet Adopted From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by us as of the specified effective date. Unless otherwise discussed, we believe that the impact of recently issued standards that are not yet effective will not have a material impact on our consolidated financial statements and disclosures.

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The entire disclosure for all significant accounting policies of the reporting entity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369 + Details
Name: | us-gaap_SignificantAccountingPoliciesTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration