3. FAIR VALUE MEASUREMENT
The following tables summarize our assets and liabilities measured at fair value on a recurring basis using the following levels of inputs as of December 31, 2021 and 2020, as indicated (in thousands): | | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at December 31, 2021 | | Total | | Level 1 | | Level 2 | | Level 3 | Assets: | | | | | | | | Cash equivalents—Money market mutual funds | $ | — | | | $ | — | | | $ | — | | | $ | — | | Equity securities, at fair value | 102,529 | | | 174 | | | — | | | 102,355 | | | | | | | | | | Trading securities held in a "rabbi trust" (1) | 179 | | | 179 | | | — | | | — | | Total assets | $ | 102,708 | | | $ | 353 | | | $ | — | | | $ | 102,355 | | Liabilities: | | | | | | | | | | | | | | | | Deferred compensation accrual "rabbi trust" (2) | $ | 188 | | | $ | 188 | | | $ | — | | | $ | — | | Total liabilities | $ | 188 | | | $ | 188 | | | $ | — | | | $ | — | |
| | | | | | | | | | | | | | | | | | | | | | | | | Fair Value Measurements at December 31, 2020 | | Total | | Level 1 | | Level 2 | | Level 3 | Assets: | | | | | | | | Cash equivalents—Money market mutual funds | $ | — | | | $ | — | | | $ | — | | | $ | — | | Equity securities, at fair value | 1,127 | | | 1,127 | | | — | | | — | | | | | | | | | | Trading securities held in a "rabbi trust" (1) | 139 | | | 139 | | | — | | | — | | Total assets | $ | 1,266 | | | $ | 1,266 | | | $ | — | | | $ | — | | Liabilities: | | | | | | | | | | | | | | | | Deferred compensation accrual "rabbi trust" (2) | $ | 148 | | | $ | 148 | | | $ | — | | | $ | — | | Total liabilities | $ | 148 | | | $ | 148 | | | $ | — | | | $ | — | |
___________________________________________ (1) — Trading securities held in a rabbi trust are included in Prepaids and other current assets and Other long-term assets, net in the consolidated balance sheets. (2) — Non-qualified deferred compensation in a rabbi trust is included in Accrued liabilities and Other long-term liabilities in the consolidated balance sheets. The activity for our Level 3 investments for the year ended December 31, 2021 is as follows:
| | | | | | | Amount | Level 3 investments at December 31, 2020 | $ | — | | Increase due to acquisition of Level 3 investments | 99,723 | | Increase in fair value of Level 3 investments | 2,632 | | Level 3 investments at December 31, 2021 | $ | 102,355 | |
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