Accounting guidance for fair value measurements specifies a hierarchy of valuation techniques based upon whether the inputs to those valuation techniques reflect assumptions other market participants would use based upon market data obtained from independent sources or reflect our own assumptions of market participant valuation. The hierarchy is broken down into three levels based on the reliability of the inputs as follows:

During 2019, 2018, and 2017 we utilized Level 1 inputs to determine the fair value of cash equivalents, and Level 3 inputs to determine the fair value of net assets acquired in business combinations (see Note 4), for our annual impairment testing (see Note 12), and our impairment testing over our disposal group (see Note 5). We did not have any transfers between Level 1 and Level 2 fair value measurements during 2019.

We classify cash on hand and deposits in banks, including commercial paper, money market accounts, and other investments with an original maturity of three months or less, that we hold from time to time, as cash and cash equivalents. We periodically have cash equivalents consisting of short-term money market funds and other investments. As of December 31, 2019 and 2018, we did not have any such cash equivalents on hand. The primary objective of our investment activities is to preserve our capital for the purpose of funding operations. We do not enter into investments for trading or speculative purposes.

At the time of sale, we establish an estimated reserve for trade, promotion, and other special price reductions such as contract pricing, discounts to meet competitor pricing, and on-time payment discounts. We also adjust receivable balances for, among other things, correction of billing errors, incorrect shipments, and settlement of customer disputes. Customers are allowed to return inventory if and when certain conditions regarding the physical state of the inventory and our approval of the return are met. Certain distribution customers are allowed to return inventory at original cost, in an amount not to exceed three percent of the prior year’s purchases, in exchange for an order of equal or greater value. Until we can process these reductions, corrections, and returns (together, the Changes) through individual customer records, we estimate the amount of outstanding Changes and recognize them by reducing revenues. We base these estimates on historical and anticipated sales demand, trends in product pricing, and historical and anticipated Changes patterns. We make revisions to these estimates in the period in which the facts that give rise to each revision become known. Future market conditions might require us to take actions to further reduce prices and increase customer return authorizations. Unprocessed Changes recognized against our gross accounts receivable balance at December 31, 2019 and 2018 totaled $29.5 million and $25.5 million, respectively. Unprocessed Changes recognized as accrued liabilities at December 31, 2019 and 2018 totaled $11.0 million and $9.1 million, respectively.

As of and for each of the three year periods ended December 31, 2019, we evaluated the collectability of accounts receivable based on the specific identification method. A considerable amount of judgment is required in assessing the realizability of accounts receivable, including the current creditworthiness of each customer and related aging of past due balances. We perform ongoing credit evaluations of our customers’ financial condition. Through these evaluations, we may become aware of a situation where a customer may not be able to meet its financial obligations due to deterioration of its financial viability, credit ratings, or bankruptcy. We record a specific reserve for bad debts against amounts due to reduce the receivable to its estimated collectible balance. We recognized bad debt expense, net of recoveries, of $0.1 million, $0.2 million, and $0.4 million in 2019, 2018, and 2017, respectively. The allowance for doubtful accounts at December 31, 2019 and 2018 totaled $2.6 million and $3.1 million, respectively.

Inventories are stated at the lower of cost or net realizable value. We determine the cost of all raw materials, work-in-process, and finished goods inventories by the first in, first out method. Cost components of inventories include direct labor, applicable production overhead, and amounts paid to suppliers of materials and products as well as freight costs and, when applicable, duty costs to import the materials and products.

We evaluate the realizability of our inventory on a product-by-product basis in light of historical and anticipated sales demand, technological changes, product life cycle, component cost trends, product pricing, and inventory condition. In circumstances where inventory levels are in excess of anticipated market demand, where inventory is deemed technologically obsolete or not saleable due to condition, or where inventory cost exceeds net realizable value, we record a charge to cost of sales and reduce the inventory to its net realizable value. The allowances for excess and obsolete inventories at December 31, 2019 and 2018 totaled $21.2 million and $17.4 million, respectively.

We record property, plant and equipment at cost. We calculate depreciation on a straight-line basis over the estimated useful lives of the related assets ranging from 10 to 40 years for buildings, 5 to 12 years for machinery and equipment, and 5 to 10 years for computer equipment and software. Construction in process reflects amounts incurred for the configuration and build-out of property, plant and equipment and for property, plant and equipment not yet placed into service. We charge maintenance and repairs—both planned major activities and less-costly, ongoing activities—to expense as incurred. We capitalize interest costs associated with the construction of capital assets and amortize the costs over the assets’ useful lives. Depreciation expense is included in costs of sales; selling, general and administrative expenses; and research and development expenses in the Consolidated Statements of Operations based on the specific categorization and use of the underlying assets being depreciated.

We review property, plant and equipment to determine whether an event or change in circumstances indicates the carrying values of the assets may not be recoverable. We base our evaluation on the nature of the assets, the future economic benefit of the assets, and any historical or future profitability measurements, as well as other external market conditions or factors that may be present. If such impairment indicators are present or other factors exist that indicate that the carrying amount of an asset may not be recoverable, we determine whether impairment has occurred through the use of an undiscounted cash flow analysis. If impairment has occurred, we recognize a loss for the difference between the carrying amount and the fair value of the asset.

For purposes of impairment testing of long-lived assets, we have identified asset groups at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities. Generally, our asset groups are based on an individual plant or operating facility level. In some circumstances, however, a combination of plants or operating facilities may be considered the asset group due to interdependence of operational activities and cash flows.

Our intangible assets consist of (a) definite-lived assets subject to amortization such as developed technology, customer relationships, certain in-service research and development, certain trademarks, backlog, and capitalized software intangible assets, and (b) indefinite-lived assets not subject to amortization such as goodwill, certain trademarks, and certain in-process research and development intangible assets. We record amortization of the definite-lived intangible assets over the estimated useful lives of the related assets, which generally range from one year or less for backlog to more than 25 years for certain of our customer relationships. We determine the amortization method for our definite-lived intangible assets based on the pattern in which the economic benefits of the intangible asset are consumed. In the event we cannot reliably determine that pattern, we utilize a straight-line amortization method.

We test our goodwill and other indefinite-lived intangible assets not subject to amortization for impairment on an annual basis as of our fiscal November month-end or when indicators of impairment exist. We base our estimates on assumptions we believe to be reasonable, but which are not predictable with precision and therefore are inherently uncertain. Actual future results could differ from these estimates.

The accounting guidance related to goodwill impairment testing allows for the performance of an optional qualitative assessment of whether it is more likely than not that the fair value of a reporting unit is less than its carrying value. Such an evaluation is made based on the weight of all available evidence and the significance of all identified events and circumstances that may influence the fair value of a reporting unit. If it is more likely than not that the fair value is less than the carrying value, then a quantitative assessment is required for the reporting unit, as described in the paragraph below. In 2019, we did not perform a qualitative assessment over any of our reporting units.

For our annual impairment test in 2019, we performed a quantitative assessment for all ten of our reporting units included in continuing operations. Under a quantitative assessment for goodwill impairment, we determine the fair value using the income approach (using Level 3 inputs) as reconciled to our aggregate market capitalization. Under the income approach, we calculate the fair value of a reporting unit based on the present value of estimated future cash flows. If the fair value of the reporting unit exceeds the carrying value of the net assets including goodwill assigned to that unit, goodwill is not impaired. If the carrying value of the reporting unit’s net assets including goodwill exceeds the fair value of the reporting unit, then we record an impairment charge based on that difference. In addition to the income approach, we calculate the fair value of our reporting units under a market approach. The market approach measures the fair value of a reporting unit through analysis of financial multiples of comparable businesses. Consideration is given to the financial conditions and operating performance of the reporting unit being valued relative to those publicly-traded companies operating in the same or similar lines of business. The fair values of all ten reporting units tested under a quantitative approach were in excess of the carrying values as of the impairment testing date, and as a result, the goodwill balances for our continuing operations reporting units were not impaired in 2019. Furthermore, goodwill was not impaired in 2018 or 2017. See Note 12 for further discussion.

We also evaluate indefinite lived intangible assets for impairment annually or at other times if events have occurred or circumstances exist that indicate the carrying values of those assets may no longer be recoverable. We compare the fair value of the asset with its carrying amount. If the carrying amount of the asset exceeds its fair value, we recognize an impairment loss in an amount equal to that excess. We did not recognize impairment charges for our indefinite lived intangible assets in 2019, 2018, or 2017. See Note 12 for further discussion.

We review intangible assets subject to amortization whenever an event or change in circumstances indicates the carrying values of the assets may not be recoverable. We test intangible assets subject to amortization for impairment and estimate their fair values using the same assumptions and techniques we employ on property, plant and equipment. We did not recognize any impairment charges for amortizable intangible assets in 2019, 2018, or 2017.

Due to its overall financial performance during the year and discontinued operations classification, we performed interim impairment tests on the Grass Valley reporting unit, which resulted in a total asset impairment of $521.4 million for the year ended December 31, 2019. We determined the estimated fair values of the assets and of the reporting unit by calculating the present values of their estimated future cash flows, which was based in part on the assumed proceeds from a divestiture of Grass Valley. See Note 12 for further discussion.

During 2017, we sold our MCS business and a 50% ownership interest in Xuzhou Hirschmann Electronics Co. Ltd (the Hirschmann JV) for a total purchase price of $40.2 million and recognized a loss on sale of the assets of $1.0 million, which was included in selling, general and administrative expenses. This loss included $2.8 million of accumulated other comprehensive losses that were recognized as a result of the sale. The $40.2 million of proceeds from the sale was collected during 2018. The MCS business was part of the Industrial Solutions segment and operated in Germany and the United States. The Hirschmann JV was an equity method investment located in China that was not included in an operating segment.

Our pension and other postretirement benefit costs and obligations are dependent on the various actuarial assumptions used in calculating such amounts. These assumptions relate to discount rates, salary growth, long-term return on plan assets, health care cost trend rates, mortality tables, and other factors. We base the discount rate assumptions on current investment yields on high-quality corporate long-term bonds. The salary growth assumptions reflect our long-term actual experience and future or near-term outlook. We determine the long-term return on plan assets based on historical portfolio results and management’s expectation of the future economic environment. Our health care cost trend assumptions are developed based on historical cost data, the near-term outlook, and an assessment of likely long-term trends. Actual results that differ from our assumptions are accumulated and, if in excess of the lesser of 10% of the projected benefit obligation or the fair market value of plan assets, are amortized over the estimated future working life of the plan participants.

We grant incentive rebates to participating customers as part of our sales programs. The rebates are determined based on certain targeted sales volumes. Rebates are paid quarterly or annually in either cash or receivables credits. Until we can process these rebates through individual customer records, we estimate the amount of outstanding rebates and recognize them as accrued liabilities and reductions in our gross revenues. We base our estimates on both historical and anticipated sales demand and rebate program participation. We charge revisions to these estimates back to accrued liabilities and revenues in the period in which the facts that give rise to each revision become known. Future market conditions and product transitions might require us to take actions to increase sales rebates offered, possibly resulting in an incremental increase in accrued liabilities and an incremental reduction in revenues at the time the rebate is offered. Accrued sales rebates at December 31, 2019 and 2018 totaled $37.2 million and $41.3 million, respectively.

We have established liabilities for environmental and legal contingencies that are probable of occurrence and reasonably estimable, the amounts of which are currently not material. A significant amount of judgment and use of estimates is required to quantify our ultimate exposure in these matters. We review the valuation of these liabilities on a quarterly basis, and we adjust the balances to account for changes in circumstances for ongoing and emerging issues.

We accrue environmental remediation costs based on estimates of known environmental remediation exposures developed in consultation with our environmental consultants and legal counsel, the amounts of which are not currently material. We expense environmental compliance costs, which include maintenance and operating costs with respect to ongoing monitoring programs, as incurred. We evaluate the range of potential costs to remediate environmental sites. The ultimate cost of site clean-up is difficult to predict given the uncertainties of our involvement in certain sites, uncertainties regarding the extent of the required clean-up, the availability of alternative clean-up methods, variations in the interpretation of applicable laws and regulations, the possibility of insurance recoveries with respect to certain sites, and other factors.

We are, from time to time, subject to routine litigation incidental to our business. These lawsuits primarily involve claims for damages arising out of the use of our products, allegations of patent or trademark infringement, and litigation and administrative proceedings involving employment matters and commercial disputes. Assessments regarding the ultimate cost of lawsuits require judgments concerning matters such as the anticipated outcome of negotiations, the number and cost of pending and future claims, and the impact of evidentiary requirements. Based on facts currently available, we believe the disposition of the claims that are pending or asserted will not have a materially adverse effect on our financial position, results of operations or cash flow.

We allocate the consideration of an acquired business to its identifiable assets and liabilities based on estimated fair values. The excess of the consideration over the amount allocated to the assets and liabilities, if any, is recorded to goodwill. We use all available information to estimate fair values. We typically engage third party valuation specialists to assist in the fair value determination of inventories, tangible long-lived assets, and intangible assets other than goodwill. The carrying values of acquired receivables and accounts payable have historically approximated their fair values as of the business combination date. As necessary, we may engage third party specialists to assist in the estimation of fair value for certain liabilities, such as deferred revenue or postretirement benefit liabilities. We adjust the preliminary acquisition accounting, as necessary, typically up to one year after the acquisition closing date as we obtain more information regarding asset valuations and liabilities assumed.

We recognize revenue consistent with the principles as outlined in the following five step model: (1) identify the contract with the customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue when (or as) each performance obligation is satisfied. See Note 3.

On July 5, 2011, the Company’s wholly-owned subsidiary, PPC, filed an action for patent infringement against Corning alleging that Corning infringed two of PPC’s patents. In July 2015, a jury found that Corning willfully infringed both patents. Following a series of appeals, we received a pre-tax amount of approximately $62.1 million from Corning on July 19, 2018. We recorded the $62.1 million of cash received as a pre-tax gain from patent litigation during 2018. Prior to 2018, we had not recognized any amounts in our consolidated financial statements related to this matter. On September 27, 2018, Corning filed a petition for certiorari review by the U.S. Supreme Court. On December 10, 2018, Corning’s certiorari review by the Supreme Court was denied, thus exhausting their opportunities for further appellate relief.

Cost of sales includes our total cost of inventory sold during the period, including material, labor, production overhead costs, variable manufacturing costs, and fixed manufacturing costs. Production overhead costs include operating supplies, applicable utility expenses, maintenance costs, and scrap. Variable manufacturing costs include inbound, interplant, and outbound freight, inventory shrinkage, and charges for excess and obsolete inventory. Fixed manufacturing costs include the costs associated with our purchasing, receiving, inspection, warehousing, distribution centers, production and inventory control, and manufacturing management. Cost of sales also includes the costs to provide maintenance and support and other professional services.

Selling, general and administrative expenses include expenses not directly related to the production of inventory. They include all expenses related to selling and marketing our products, as well as the salary and benefit costs of associates performing the selling and marketing functions. Selling, general and administrative expenses also include salary and benefit costs, purchased services, and other costs related to our executive and administrative functions.

We compensate certain employees and non-employee directors with various forms of share-based payment awards and recognize compensation costs for these awards based on their fair values. We estimate the fair values of certain awards, primarily stock appreciation rights (SARs), on the grant date using the Black-Scholes-Merton option-pricing formula, which incorporates certain assumptions regarding the expected term of an award and expected stock price volatility. We develop the expected term assumption based on the vesting period and contractual term of an award, our historical exercise and cancellation experience, our stock price history, plan provisions that require exercise or cancellation of awards after employees terminate, and the extent to which currently available information indicates that the future is reasonably expected to differ from past experience. We develop the expected volatility assumption based on historical price data for our common stock. We estimate the fair value of certain restricted stock units with service vesting conditions and performance vesting conditions based on the grant date stock price. We estimate the fair value of certain restricted stock units with market conditions using a Monte Carlo simulation valuation model with the assistance of a third party valuation firm.

Income taxes are provided based on earnings reported for financial statement purposes. The provision for income taxes differs from the amounts currently payable to taxing authorities because of the recognition of revenues and expenses in different periods for income tax purposes than for financial statement purposes. Income taxes are provided as if operations in all countries, including the U.S., were stand-alone businesses filing separate tax returns.

We recognize deferred tax assets resulting from tax credit carryforwards, net operating loss carryforwards, and deductible temporary differences between taxable income on our income tax returns and pretax income on our financial statements. Deferred tax assets generally represent future tax benefits to be received when these carryforwards can be applied against future taxable income or when expenses previously reported in our Consolidated Financial Statements become deductible for income tax purposes. A deferred tax asset valuation allowance is required when some portion or all of the deferred tax assets may not be realized. At December 31, 2019 the valuation allowance of $50.4 million was primarily related to net operating losses and foreign tax credits that we do not expect to realize.

Our effective tax rate is based on expected income, statutory tax rates, and tax planning opportunities available to us in the various jurisdictions in which we operate. Significant judgment is required in determining our effective tax rate and in evaluating our tax positions. We establish accruals for uncertain tax positions when we believe that the full amount of the associated tax benefit may not be realized. To the extent we were to prevail in matters for which accruals have been established or would be required to pay

On December 22, 2017, the “Tax Cuts and Jobs Act” (the “Act”) was signed into law, making significant changes to the U.S. Internal Revenue Code. During 2019, the United States Treasury issued final and proposed regulations with respect to certain aspects related to the Act. Additional guidance provided in these regulation resulted in a tax adjustment in the fourth quarter of 2019. The total tax provision expense in 2019 included a $10.0 million tax expense associated with the increase to the valuation allowance against foreign tax credit carryovers that were no longer expect to be able to realize based upon the new proposed tax regulations. See Note 17, Income Taxes, in the accompanying notes to our consolidated financial statements.

In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases ("ASU 2016-02"), a leasing standard for both lessees and lessors that supersedes the lease requirements in Accounting Standards Codification (ASC) Topic 840, "Leases." Under its core principle, a lessee will recognize a right-of-use (ROU) asset and lease liability on the balance sheet for nearly all leased assets, and additional disclosures are required to enable users of financial statements to assess the amount, timing, and uncertainty of cash flows arising from leases. We adopted ASU 2016-02 on January 1, 2019 using the permitted transition method issued in July 2018, under ASU No. 2018-11 (“ASU 2018-11”), Leases: Targeted Improvements, which provides an additional (and optional) transition method for adopting the new lease standard. Furthermore, we elected the following practical expedients and accounting policy elections upon adoption: (i) the package of practical expedients as defined in ASU 2016-02, (ii) the short-term lease accounting policy election, (iii) the practical expedient to not separate non-lease components from lease components, and (iv) the easement practical expedient, which permits an entity to continue applying its current policy for accounting for land easements that existed as of the effective date of ASU 2016-02. Excluding the impact of our Grass Valley disposal group, the adoption of ASU 2016-02 on January 1, 2019 resulted in the recognition of right-of-use assets of approximately $70.7 million and lease liabilities for operating leases of approximately $77.3 million on the Consolidated Balance Sheet, with no material impact to the Consolidated Statements of Operations or Consolidated Cash Flow Statements. The difference between the initial lease liabilities and the ROU assets is related primarily to previously existing lease liabilities. See Note 11 for further information regarding the impact of the adoption of ASU 2016-02 on the Company's financial statements.

In August 2017, the FASB issued Accounting Standards Update No. ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities (“ASU 2017-12”). The new guidance better aligns an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The new guidance also makes certain targeted improvements to simplify the application of hedge accounting guidance and ease the administrative burden of hedge documentation requirements and assessing hedge effectiveness. The standard is effective for fiscal years beginning after December 15, 2018. We adopted ASU 2017-12 effective January 1, 2019. The adoption had no impact on our results of operations.

In February 2018, the FASB issued ASU No. 2018-02 (“ASU 2018-02”), Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. ASU 2018-02 provides an option to allow reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The new guidance is effective for annual and interim periods beginning after December 15, 2018. We adopted ASU 2018-02 effective January 1, 2019, and elected to not reclassify the income tax effects of the Act from accumulated other comprehensive income to retained earnings. The adoption had no impact on our results of operations.

In June 2018, the FASB issued ASU No. 2018-07 (“ASU 2018-07”), Improvements to Nonemployee Share-Based Payment Accounting. The amendments in ASU 2018-07 expand the scope of Topic 718, Compensation - Stock Compensation, to include share-based payment transactions for acquiring goods and services from non-employees, and provide that non-employee share-based payment awards be measured at their grant-date fair value and the probability of satisfying performance conditions be taken into account when non-employee share-based payment awards contain such conditions. The standard is effective for fiscal years beginning after December 15, 2018. We adopted ASU 2018-07 effective January 1, 2019. The adoption had no impact on our results of operations.

In August 2018, the Securities and Exchange Commission (“SEC”) adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification, amending certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. Additionally, the amendments expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders' equity presented in the balance sheet must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period presented. This final rule was effective on November 5, 2018. We implemented SEC Release No. 33-10532 effective January 1, 2019, which had no impact on our results of operations.

In June 2016, the FASB issued Accounting Standards Update No. 2016-13 (“ASU 2016-13”), Financial Instruments - Credit Losses. The main provisions of ASU 2016-13 provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date, and require a financial asset (or a group of financial assets) measured at amortized cost basis to be presented at the net amount expected to be collected. The new standard will be effective for us beginning January 1, 2020. We expect the adoption will result in an increase to our allowance for doubtful accounts for continuing operations of approximately $1.0 million, and an increase for discontinued operations of approximately $2.0 million.