| Fair Value Measurements |
Fair Value Measurements We measure certain financial instruments at fair value using a fair value hierarchy. In the hierarchy, assets are classified based on the lowest level inputs used in valuation into the following categories: | | • | Level 1 — Quoted prices in active markets for identical assets and liabilities; |
| | • | Level 2 — Observable inputs including quoted market prices for similar assets and liabilities in active markets, quoted prices for identical assets and liabilities in inactive markets, or inputs that are corroborated by observable market data; and |
| | • | Level 3 — Unobservable inputs. |
The following tables summarize assets that are measured at fair value on a recurring basis: | | | | | | | | | | | | | | | | | | March 31, 2019 | (in thousands) | Level 1 | | Level 2 | | Level 3 | | Total | Cash and cash equivalents | | | | | | | | Money market funds | $ | 20,732 |
| | $ | — |
| | $ | — |
| | $ | 20,732 |
| Commercial paper | — |
| | 4,489 |
| | — |
| | 4,489 |
| | $ | 20,732 |
| | $ | 4,489 |
| | $ | — |
| | $ | 25,221 |
| | | | | | | | | Short-term investments | | | | | | | | Commercial paper | $ | — |
| | $ | 66,166 |
| | $ | — |
| | $ | 66,166 |
| Corporate bonds | — |
| | 12,678 |
| | — |
| | 12,678 |
| U.S. Treasury and agency obligations | — |
| | 52,170 |
| | — |
| | 52,170 |
| | $ | — |
| | $ | 131,014 |
| | $ | — |
| | $ | 131,014 |
|
| | | | | | | | | | | | | | | | | | December 31, 2018 | (in thousands) | Level 1 | | Level 2 | | Level 3 | | Total | Cash and cash equivalents | | | | | | | | Money market funds | $ | 38,022 |
| | $ | — |
| | $ | — |
| | $ | 38,022 |
| | $ | 38,022 |
| | $ | — |
| | $ | — |
| | $ | 38,022 |
| | | | | | | | | Short-term investments | | | | | | | | Commercial paper | $ | — |
| | $ | 79,634 |
| | $ | — |
| | $ | 79,634 |
| Corporate bonds | — |
| | 16,119 |
| | — |
| | 16,119 |
| U.S. Treasury and agency obligations | — |
| | 22,366 |
| | — |
| | 22,366 |
| | $ | — |
| | $ | 118,119 |
| | $ | — |
| | $ | 118,119 |
|
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