The Company amortizes its definite-lived intangible asset using the straight-line method, which is considered the best estimate of economic benefit, over its estimated useful life of six years. The Company recorded $36.0 million in amortization expense during the years ended December 31, 2022 and 2021, and $32.6 million in amortization expense during the year ended December 31, 2020 related to the developed product rights for Auryxia. Estimated future amortization expense for the intangible asset as of December 31, 2022 is as follows (in thousands):

In the second quarter of 2020, in connection with a routine business review, the Company reduced its short-term and long-term Auryxia revenue forecast. This reduction was primarily driven by the compounding impact of the September 2018 CMS decision that rescinded Medicare Part D coverage of Auryxia for the IDA Indication and the related imposition by CMS of a prior authorization requirement for Auryxia for the Hyperphosphatemia Indication. As a result, the Company determined indicators of impairment existed for the developed product rights for Auryxia and performed an undiscounted cash flow analysis pursuant to ASC 360-10, Impairment or Disposal of Long-lived Assets, to determine if the cash flows expected to be generated by the Auryxia asset group over the estimated remaining useful life of the primary assets were sufficient to recover the carrying value of the Auryxia asset group. Based on this analysis, the undiscounted cash flows were not sufficient to recover the carrying value of the Auryxia asset group. As a result, the Company was required to perform Step 3 of the impairment test to determine the fair value of the Auryxia asset group.

To estimate the fair value, the Company performed a business enterprise valuation for the Auryxia asset group using the income approach, which is based on a discounted cash flow analysis and calculates the fair value by estimating the after-tax cash flows attributable to the asset group and then discounting the after-tax cash flows to present value using a risk-adjusted discount rate. Key estimates and assumptions used in the valuations included projected revenues and expenses related to the asset, estimated contributory asset charges, and a risk-adjusted discount rate of 9.5% to calculate the present value of the future expected cash inflows. The Company believes its assumptions are consistent with the plans and estimates that a market participant would use to manage the business. The discount rates used are intended to reflect the risks inherent in future cash flow projections and were based on an estimate of the weighted average cost of capital, or WACC, of market participants relative to the Auryxia asset group.

As a result of this analysis, the fair value of the Auryxia asset group was below its carrying value, and the Company recorded an impairment charge of $114.4 million during the three months ended June 30, 2020 and made a corresponding adjustment to the estimated useful life of the developed product rights for Auryxia from nine years to seven years. The impairment charge has been entirely allocated to the Company’s only intangible asset, the developed product rights for Auryxia, as all other long-lived assets had fair values that were either equal to or greater than their carrying value. Per ASC 360-10, the carrying amount of a long-lived asset of the group would not be reduced below its fair value. The Company believes its assumptions used to determine the fair value of the Auryxia asset group are reasonable. In the event the estimates and assumptions used in the valuation of the Auryxia asset group, including the forecasted projections, change in the future, additional impairment charges could be recorded in the future.

In the fourth quarter of 2020, as part of the Company's routine forecasting process, the Company reassessed and prospectively adjusted the estimated useful life of the developed product rights for Auryxia from seven years to six years. This was not deemed an impairment indicator as of December 31, 2020.

Goodwill was $59.0 million as of December 31, 2022 and 2021. The Company operates in one operating segment which the Company considers to be the only reporting unit. Goodwill is evaluated for impairment at the reporting unit level on an annual basis as of October 1, and more frequently if indicators are present or changes in circumstances suggest that an impairment may exist. Events that could indicate impairment and trigger an impairment assessment include, but are not limited to, an adverse change in current economic or market conditions, including a significant prolonged decline in market capitalization, a significant adverse change in legal factors, unexpected adverse business conditions, and an adverse action by a regulator. During the year ended December 31, 2022, the Company evaluated business factors, including the receipt of the CRL from the FDA for vadadustat, the Company's market capitalization as impacted by a recent decline in the Company's stock price, the impact of the Otsuka Termination Agreement on the Company's future cash flows, and the impact of the BioVectra Termination

Agreement to the Company's excess purchase commitment liability to determine if there were events or changes in circumstance to indicate that the fair value of the reporting unit was less than its carrying value. The Company performed a qualitative impairment assessment of the Company's goodwill balance as the year ended December 31, 2022. The Company determined that it was not more likely than not that the fair value of the reporting unit was less than its carrying value and, therefore, did not perform a further quantitative impairment test.

The Company's qualitative assessments were based on the Company's estimates and assumptions, a number of which are dependent on external factors and actual results may differ materially from these estimates. In addition, the future occurrence of events including, but not limited to, an adverse change in current economic and market conditions, including a significant prolonged decline in market capitalization, a significant adverse change in legal factors, unexpected adverse business conditions and an adverse action or assessment by a regulator could indicate potential impairment and trigger an impairment assessment of goodwill, which could result in an impairment of goodwill. As a result of the significance of goodwill, the Company's results of operations and financial position in a future period could be negatively impacted should an impairment test be triggered that results in an impairment of goodwill.