15. Non-Marketable Investments

We held investments in privately held companies with a carrying value of $55.0 million and $43.6 million as of December 31, 2019 and 2018, respectively. Our share of gains and losses in equity method investments was not material for the years ended December 31, 2019, 2018, and 2017, and is included in other income (expense), net in our consolidated statements of operations. Non-marketable investments are included within other assets on the consolidated balance sheet. Such investments are reviewed periodically for impairments. Impairment recorded for the year ended December 31, 2019 was not material. We recorded impairments of $7.2 million for the year ended December 31, 2018 million within other income (expense), net in the consolidated statements of operations. No impairments were recorded in the year ended December 31, 2017. Additionally, we recognized gains on non-marketable investments of $20.8 million within other income (expense), net on the consolidated statement of operations.