The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect (1) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the balance sheet dates and (2) the reported amounts of revenues and expenses during the reporting periods. We base our estimates on historical experience, currently available information and various other assumptions that we believe are reasonable under the circumstances. Actual results could differ from these estimates.

We account for revenue in accordance with Accounting Standards Codification ("ASC") Topic 606, “Revenue from Contracts with Customers.” Collaborative revenue contracts, for which the collaboration partner meets the definition of a customer, are recorded in accordance with ASC Topic 606; otherwise, the collaborative arrangements are recorded in accordance with ASC 808, "Collaborative Arrangements". See Note 5 for further discussion.

At times, the Company has invested a portion of its excess cash in short-term investments. The Company's short-term investment accounting policy is that securities with maturities greater than 90 days at the time of purchase that are available for operations in the next 12 months are classified as short-term investments. The Company’s short-term investments primarily consist of investment grade bonds, certificates of deposit, commercial paper, and short maturity bond funds, all with a remaining maturity of generally less than twelve months at the date of purchase and classified as available-for-sale. Interest and dividends on these investments are recorded into income when earned.

Available-for-sale securities, which consist of debt securities, are carried at fair value with unrealized gains and losses, net of related tax, reported in other comprehensive (loss) income. Adjustments to the fair value of investments classified as available-for-sale are recorded as an increase or decrease in accumulated other comprehensive income (loss) in shareholders’ equity. Impairment of available-for-sale securities that is attributable to credit losses is recognized as an allowance for credit losses, net of taxes, in the consolidated statement of operations in the period in which a credit loss is identified. The Company periodically evaluates its investment for credit losses.

Upon making an investment in an entity, we assess whether the entity is a VIE. The determination of whether an entity in which we hold a direct or indirect variable interest is a VIE is based on several factors, including whether the entity’s total equity investment at risk upon inception is sufficient to finance the entity’s activities without additional subordinated financial support. We make judgments regarding the sufficiency of the equity at risk based first on a qualitative analysis, and then a quantitative analysis, if necessary.

We analyze any investments in VIEs to determine if we are the primary beneficiary. We perform this assessment at the time that we become involved with a VIE and reevaluate our conclusion upon the occurrence of a reconsideration event. In evaluating whether we are the primary beneficiary, we evaluate our direct and indirect economic interests in the entity. Determining which reporting entity, if any, is the primary beneficiary of a VIE is primarily a qualitative approach focused on identifying which reporting entity has both (1) the power to direct the activities of a VIE that most significantly impact such entity’s economic performance and (2) the obligation to absorb losses or the right to receive benefits from such entity that could potentially be significant to such entity. Performance of such analysis requires the exercise of judgment, and we consider a variety of factors in identifying the entity that holds the power to direct matters that most significantly impact a VIE’s economic performance including, but not limited to, the ability to direct a VIE’s operating decisions and activities. In addition, we consider the rights of other investors to participate in those decisions.

We concluded that our investments in Theradaptive and the National Additive Manufacturing Innovation ("NAMI") joint venture are each investments in a VIE. These entities in which we have invested are not consolidated because we concluded that the Company is not the primary beneficiary. As of December 31, 2023, our maximum exposure to losses associated with these VIEs is limited to the $13,247 carrying value of our investments in the VIEs, which is included in other assets on our consolidated balance sheets. Refer to Note 10 for additional details regarding our investments in Theradaptive and NAMI. We have no other investments in unconsolidated entities that have been determined to be VIEs.

We recognize investments in equity securities without a readily determinable fair value at cost minus impairment. We assess these investments for potential impairment if an event occurs or circumstances change that would indicate the carrying amount may be impaired. Impairments of equity securities without a readily determinable fair value are recorded to interest and other income (expense), net in the consolidated statements of operations in the period in which they become impaired. Declines in the fair value of investments in debt securities due to credit losses are recorded as an allowance for credit losses in the consolidated statement of operations in the period in which a credit loss is identified.

For the years ended December 31, 2023, 2022, and 2021, we recorded impairment charges of $0, $2,900 and $0, respectively, related to non-current investments. The aggregate carrying amount of all non-current investments totaled $26,829 and $13,668 at December 31, 2023 and 2022, respectively, and is included in other assets on our consolidated balance sheets.

Under the equity method of accounting, this initial investment was recorded at cost, and the investment is subsequently adjusted for the Company’s proportionate share of the net earnings or losses and other comprehensive income or loss of the investee. Intra-entity profits or losses associated with the Company’s equity method investment are eliminated until realized by the investee in transactions with third parties. Income or loss from this investment is recorded as a separate line item in the consolidated statements of operations on a three-month lag. We evaluate material events occurring during the three-month lag period to determine whether the effects of such events should be disclosed in our financial statements. The Company evaluates its investment in the joint venture for impairment whenever events or changes in circumstances indicate that the carrying amount of the investment may not be recoverable. Refer to Note 10.

Trade accounts receivable are recorded at the invoiced amount and do not bear interest. In evaluating the collectability of accounts receivable, we assess a number of factors, including specific customers’ ability to meet their financial obligations to us, the length of time receivables are past due, historical collection experience, current economic conditions, and reasonable and supportable forecasts. Based on these assessments, we may record a reserve for specific customers, as well as a general reserve and allowance for expected credit losses. If circumstances related to specific customers change, or economic conditions deteriorate such that our past collection experience is no longer relevant, our estimate of the recoverability of accounts receivable could be further reduced from the levels provided for in the consolidated financial statements. As of December 31, 2023, no single customer represented more than 10% of our consolidated accounts receivable balance. As of December 31, 2022, one customer represented greater than 10% of our consolidated accounts receivable balance.

Inventories are stated at the lower of cost or net realizable value, with cost reflecting standard cost, which approximates the first-in, first-out method. Capitalized inventory costs include materials, labor, and manufacturing overhead that relate to the acquisition of raw materials and production into finished goods. The Company regularly reviews inventory for excess and obsolescence and records a provision to write down inventory to its net realizable value when carrying value is in excess of such value.

Property and equipment are recorded at cost and are depreciated over their estimated useful lives using the straight-line method. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the determination of net income or loss. Repairs and maintenance costs are expensed as incurred.

We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of the asset may not be recoverable. Recoverability is assessed for the carrying value of assets held for use based on a review of undiscounted projected cash flows. Impairment losses, where identified, are measured as the excess of the carrying value of a long-lived asset over its estimated fair value as determined by discounted projected cash flows. Refer to Note 7 for details regarding impairment charges that were recorded related to tangible long-lived assets with finite lives for the years ended December 31, 2023, 2022, and 2021.

Intangible assets include patents, trade names, customer relationships, acquired technology, and IPR&D. Intangible assets with a finite life are (1) amortized on a straight-line basis, with estimated useful lives typically ranging from 2 to 20 years, and (2) assessed for impairment whenever events or changes in circumstances indicate that their carrying value may not be recoverable, consistent with the Company's accounting policy for other long-lived assets with a finite life. Amortization is recognized within selling, general and administrative expense on the consolidated statements of operations.

Acquired IPR&D represents the fair value assigned to those research and development ("R&D") projects that were acquired in a business combination for which the related products have not received regulatory approval or commercial viability and have no alternative future use. IPR&D is capitalized at its fair value as an indefinite-lived intangible asset, and any development costs incurred after the acquisition are expensed as incurred. The fair value of IPR&D is determined by estimating the future cash flows of each project and discounting the net cash flows back to their present values. Upon achieving regulatory approval or commercial viability for the related product, the indefinite-lived intangible asset is accounted for as a finite-lived asset and is amortized on a straight-line basis over the estimated useful life. If the project is not completed or is terminated or abandoned, the Company may have to recognize an impairment related to the IPR&D, which is charged to expense. Indefinite-lived intangible assets are tested for impairment annually in the fourth quarter of the fiscal year and whenever events or changes in circumstances indicate that the carrying amount may be impaired. Impairment is calculated as the excess of the asset’s carrying value over its fair value. Fair value is generally determined using a discounted future cash flow analysis. IPR&D with no alternative future use acquired outside of a business combination is expensed immediately.

Goodwill is the excess of the cost of an acquired entity over the amounts assigned to the assets acquired and liabilities assumed in a business combination. Goodwill is not amortized. Goodwill is tested for impairment annually, and is tested for impairment between annual tests if an event occurs or circumstances change that would indicate the carrying amount may be impaired. Impairment testing for goodwill is performed at the reporting unit level, with all goodwill assigned to a reporting unit.

During the fourth quarter of 2023, we elected to change the annual goodwill impairment testing date for each of our reporting units from November 30th to November 1st and, accordingly, we have performed our impairment tests for the current fiscal year as of November 1, 2023. The Company does not believe that this change to the annual impairment testing date represents a material change in the method of applying an accounting principle. This voluntary change is preferable because it provides management with sufficient time to complete goodwill impairment tests in advance of the Company’s year-end financial reporting and provides additional time for the execution of key controls and management review over the significant estimates and judgements inherent in the performance of the test. This change to the goodwill impairment testing date has not been applied retrospectively as it is impracticable to do so without applying hindsight when developing key assumptions and estimates required to perform the test.

The testing of goodwill for impairment requires the Company to make several estimates related to projected future cash flows to determine the fair value of the reporting units to which goodwill has been assigned. The Company determines whether each reporting unit's fair value exceeds its carrying amount, including goodwill, utilizing a discounted cash flow analysis and other valuation techniques, as deemed appropriate. Internal operational budgets and long-range strategic plans are used as a basis for the cash flow analysis. The Company also utilizes assumptions related to working capital, capital expenditures, and terminal growth rates. The discount rate applied to the cash flow analysis is based on the weighted average cost of capital (“WACC”) for each reporting unit. An impairment is recognized when the carrying amount of the reporting unit’s net assets exceeds the estimated fair value of the reporting unit.

We follow the provisions of ASC 450, “Contingencies,” which requires that an estimated loss from a loss contingency be accrued by a charge to income if (1) it is probable that an asset has been impaired or that a liability has been incurred and (2) the amount of the loss can be reasonably estimated. Legal costs related to the defense or settlement of a loss contingency are expensed when such costs are incurred and, accordingly, future legal costs expected to be incurred are not accrued as part of the liability recorded when a loss contingency has been deemed probable and estimable.

The local currency in which a subsidiary operates is generally considered its functional currency for those subsidiaries domiciled outside the United States ("foreign subsidiaries"). The functional currency financial statements of foreign subsidiaries are translated to U.S. dollars ("USD") in connection with the preparation of the Company's consolidated financial statements. Assets and liabilities of foreign subsidiaries are translated to USD at month-end exchange rates applicable to the reporting period. Income and expense items are translated to USD monthly using monthly average exchange rates. The effects of translating a foreign subsidiary's financial statements are recorded as currency translation adjustments and reported as a component of accumulated other comprehensive income (loss) in shareholders’ equity.

Foreign currency transactions are those transactions whose terms are denominated in a currency other than an entity's functional currency. Foreign currency transactions that remain unsettled as of the end of a reporting period must be remeasured into the entity's functional currency, resulting in the recognition of a gain or loss when a change in exchange rate has occurred subsequent to the date on which the transaction was originally recognized or was most recently remeasured. The Company recognizes foreign currency transaction gains and losses within interest and other income (expense), net on its consolidated statements of operations. See Note 18.

We are exposed to market risk from changes in interest rates, foreign currency exchange rates and commodity prices, which may adversely affect our results of operations and financial condition. We seek to minimize these risks through regular operating and financing activities and, when we consider it to be appropriate, through the use of derivative financial instruments. We do not purchase, hold or sell derivative financial instruments for trading or speculative purposes.

We may use derivative financial instruments to manage our exposure to changes in interest rates on outstanding debt instruments. For those financial instruments that qualify for cash flow hedge accounting treatment under ASC 815, “Derivatives and Hedging,”, and where we elect to prepare and maintain the documentation required to qualify for cash flow hedge accounting treatment, gains and losses (realized or unrealized) are recognized in accumulated other comprehensive income (loss) and are reclassified into earnings when the underlying transaction is recognized in net earnings. Depending on the fair value at the end of the reporting period, derivatives are recorded either in prepaid and other current assets or in accrued and other liabilities on the consolidated balance sheets.

We and our subsidiaries conduct business in various countries using both functional currencies and other currencies to effect cross-border transactions. As a result, we and our subsidiaries are subject to the risk that fluctuations in foreign currency exchange rates between the dates that non-functional currency transactions are entered into and their respective settlement dates will result in a foreign currency exchange gain or loss. When practicable, we endeavor to match assets and liabilities in the same currency on our U.S. balance sheet and those of our subsidiaries in order to reduce these risks. We may enter into foreign currency exchange contracts to hedge the exposure arising from foreign currency transactions.

For our hedges of foreign currency exchange rates and commodity prices, we have elected to not prepare and maintain the documentation to qualify for hedge accounting treatment under ASC 815, “Derivatives and Hedging.” Accordingly, changes in fair value are recognized in interest and other income (expense), net on the consolidated statements of operations and, depending on the fair value at the end of the reporting period, derivatives are recorded either in prepaid expenses and other current assets or in accrued and other liabilities on the consolidated balance sheets.

R&D costs, consisting primarily of employee compensation, operating supplies, facility costs and depreciation, are expensed as incurred. When the Company is reimbursed by a collaboration partner for work the Company performs, it records the costs incurred as R&D expense and the related reimbursement as a reduction to R&D expense in its consolidated statements of operations.

Basic earnings (loss) per share is calculated using the weighted-average number of common shares outstanding during each period. Diluted earnings per share is calculated based upon the inclusion of additional dilutive and potentially dilutive shares, which include shares issuable upon exercise of outstanding stock options, upon vesting of employee restricted stock-based awards, upon the accrual of incentive compensation to be paid in shares (if any performance-based conditions have been satisfied as of the end of the reporting period), and to settle the portion of the convertible notes that may be settled in shares (where the conversion of such instruments would be dilutive). See Note 20.

We sponsor a retirement benefit for one of our non-U.S. subsidiaries in the form of a defined benefit pension plan. Accounting standards require the cost of providing this pension benefit be measured on an actuarial basis. Actuarial gains and losses resulting from both normal year-to-year changes in valuation assumptions and differences between assumptions and actual experience are deferred and amortized. The application of these accounting standards require us to make assumptions and judgements that can significantly affect these measurements. Our critical assumptions in performing these actuarial valuations include the selection of the discount rate to determine the present value of the pension obligations, which affects the amount of pension expense recorded in any given period. Changes in the discount rate could have a material effect on our reported pension obligations and related pension expense. See Note 14.

We recognize compensation expense for our stock-based compensation programs, which provide for the issuance of stock options, restricted stock, restricted stock units (“RSU”), performance-based awards and market-based awards. The fair value of service-based awards is estimated at the grant date and recognized as expense ratably over the requisite service period of the award.

The fair value of performance-based awards is estimated on the grant date and expensed over an implicit or explicit service period when the performance condition is deemed probable of achievement. Performance-based awards that cliff vest are expensed ratably using the straight-line method; whereas, performance-based awards with graded vesting features are expensed using the graded vesting method. Stock compensation expense recorded for performance-based awards is reversed if the performance condition is no longer deemed probable of achievement or ultimately is not met. Some RSUs are granted with a performance measure derived from non-GAAP-based management targets or non-financial targets. Depending on our performance with respect to these metrics, the number of RSUs earned may be less than, equal to or greater than the original number of RSUs awarded, subject to a payout range.

The fair value of awards with market conditions ("market-based awards") is determined using a Monte Carlo valuation model and is expensed over an implicit or explicit service period regardless of whether the market condition is probable of achievement or not. Market-based awards that cliff vest are expensed ratably using the straight-line method; whereas, market-based awards with graded vesting features are expensed using the graded vesting method. Stock compensation expense is not reversed if the market condition is not met.

Income taxes are accounted for under the asset and liability method. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for tax benefit carryforwards. Our deferred income tax assets and liabilities at the end of each period are determined using enacted tax rates.

We establish a valuation allowance for those jurisdictions in which the expiration date of tax benefit carryforwards or projected taxable earnings leads us to conclude that it is “more likely than not” that a deferred tax asset will not be realized. This evaluation process includes the consideration of all available evidence regarding historical results and future projections, including the estimated timing of reversals of existing taxable temporary differences and potential tax planning strategies. Once a valuation allowance is established, it is maintained until a change in factual circumstances gives rise to sufficient income of the appropriate character and timing that will allow a partial or full utilization of the deferred tax asset.

Some leases include the option to purchase the leased asset, terminate the lease or extend the lease for one or more years. These options are considered in the determination of the estimated lease term when it is reasonably certain that an option will be exercised. Our leases do not contain any material residual value guarantees or material restrictive covenants.

Certain of our leases include variable costs. Variable costs include non-lease components that are incurred based upon actual terms, rather than contractually fixed amounts. In addition, variable costs are incurred for lease payments that are indexed to a change in rate or index. Because the right-of-use ("ROU") assets recorded on the balance sheet are determined based upon factors considered at the lease commencement date, subsequent changes in the rate or index that were not contemplated in the ROU asset balances at lease commencement result in variable expenses being recorded when these expenses are incurred during the lease term. See Note 11.

In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") No. 2023-07, "Segment Reporting (Topic 280) - Improvements to Reportable Segment Disclosures." This ASU expands upon existing reportable segment disclosure requirements by requiring the disclosure of significant reportable segment expenses that are regularly provided to the Chief Operating Decision Maker (“CODM”) and included within each reported measure of a segment's profit or loss, as well as conforming interim period disclosures with annual period disclosures. This ASU also requires disclosure of the title and position of the individual identified as the CODM and an explanation of how the CODM uses the reported measures of a segment’s profit or loss in assessing segment performance and deciding how to allocate resources. The ASU is effective for annual periods beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Adoption of the ASU should be applied retrospectively to all prior periods presented in the financial statements. Early adoption is also permitted. Upon adoption, this ASU is expected to result in the inclusion of additional segment-related disclosures in the footnotes to our consolidated financial statements. We are evaluating the provisions of this ASU and currently expect to adopt the new annual disclosure requirements as of the fourth quarter of our fiscal year ending December 31, 2024.

In December 2023, the FASB issued ASU No. 2023-09, "Income Taxes (Topic 740) - Improvements to Income Tax Disclosures." The ASU requires disaggregated information about a reporting entity’s effective tax rate reconciliation, as well as additional information on income taxes paid. The ASU is effective on a prospective basis for annual periods beginning after December 15, 2024. Early adoption is also permitted for annual financial statements that have not yet been issued or made available for issuance. Upon adoption, this ASU is expected to result in the inclusion of additional tax-related disclosures in the footnotes to our consolidated financial statements.

In October 2021, the Financial Accounting Standard Board ("FASB") issued ASU 2021-08, "Business Combinations (Topic 805) - Accounting for Contract Assets and Contract Liabilities from Contracts with Customers", which amends ASC 805 to add contract assets and contract liabilities to the list of exceptions to the recognition and measurement principles that apply to business combinations and to “require that an entity (acquirer) recognize and measure contract assets and contract liabilities acquired in a business combination in accordance with ASC 606.” While primarily related to contract assets and contract liabilities that were accounted for by the acquiree in accordance with ASC 606, “the amendments also apply to contract assets and contract liabilities from other contracts to which the provisions of ASC 606 apply, such as contract liabilities from the sale of nonfinancial assets within the scope of Subtopic 610-20.” For public business entities, the amendments in this ASU became effective for fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. Early adoption of the amendments was permitted. The Company early adopted this standard in the first quarter of 2022, and it did not have an impact on its results of operations, cash flows or financial position.

In August 2020, the FASB issued ASU 2020-06, "Debt - Debt with Conversion and Other Options (Subtopic 470-20)," and "Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40)," which simplifies the accounting for convertible instruments by reducing the number of accounting models available for convertible instruments. This guidance also eliminates the treasury stock method to calculate diluted earnings per share for convertible instruments and requires the use of the if-converted method. For public companies, this guidance became effective for fiscal years beginning after December 15, 2021 and interim periods within those fiscal years. Early adoption was permitted. The Company early adopted the standard as of January 1, 2021 and applied this guidance to the convertible senior notes issued in November 2021. See Note 14.

In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes,” which simplifies the accounting for income taxes by eliminating some exceptions to the general approach in ASC 740, "Income Taxes." It also clarifies certain aspects of the existing guidance to promote more consistent application. This standard became effective for calendar-year public business entities in 2021 and interim periods within that year, and early adoption was permitted. The Company adopted this guidance during the first quarter of 2021. The implementation did not have a material effect on our financial position, results of operations or cash flows.