15. Non-Marketable Investments

We held investments in privately held companies with a carrying value of $169.5 million and $55.0 million as of December 31, 2020 and 2019, respectively, which consist primarily of equity securities. Non-marketable investments are included within other assets on the consolidated balance sheet. Such investments are reviewed periodically for impairments. We recorded impairments of $29.5 million for the year ended December 31, 2020 and $7.2 million for the year ended December 31, 2018, within other income (expense), net in the consolidated statements of operations. The impairment recorded for the year ended December 31, 2019 was not material. Additionally, we recognized gains on non-marketable investments of $42.4 million and $20.8 million for the years ended December 31, 2020 and 2019, respectively, within other income (expense), net on the consolidated statement of operations. The gains on non-marketable investments for the year ended December 31, 2018 were not material.