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Fair Value Measurements and Available for Sale Investments (Tables) | 9 Months Ended
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Sep. 30, 2019
Fair Value Measurements And Available For Sale Investments [Abstract] |
Assets Measured at Fair Value on Recurring Basis | The following table presents the hierarchy for assets measured at fair value on a recurring basis as of September 30, 2019 and December 31, 2018 (in thousands):
| Fair Value Measurements at End of Period Using: |
|  |  |  |  |  | Quoted Market |  |  | Significant |  |  | Significant |
|  |  |  |  |  | Prices for |  |  | Other Observable |  |  | Unobservable |
|  | Total |  |  | Identical Assets |  |  | Inputs |  |  | Inputs |
|  | Fair Value |  |  | (Level 1) |  |  | (Level 2) |  |  | (Level 3) |
As of September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market funds |  | $ | 35,756 |  |  | $ | 35,756 |  |  | $ | — |  |  | $ | — |
U.S. Treasury and agency securities |  |  | 199,500 |  |  |  | 199,500 |  |  |  | — |  |  |  | — |
Commercial paper |  |  | 30,985 |  |  |  | — |  |  |  | 30,985 |  |  |  | — |
Corporate debt securities |  |  | 99,892 |  |  |  | — |  |  |  | 99,892 |  |  |  | — |
As of December 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market funds |  | $ | 17,295 |  |  | $ | 17,295 |  |  | $ | — |  |  | $ | — |
U.S. Treasury securities |  |  | 123,439 |  |  |  | 123,439 |  |  |  | — |  |  |  | — |
Schedule of Available for Sale Investments by Security Type | The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in marketable securities and long-term investments as of September 30, 2019 are as follows (in thousands):
|  |  |  |  |  | Gross |  |  | Gross |  |  |  |  |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  | Total |
|  | Cost |  |  | Gains |  |  | Losses |  |  | Fair Value |
Marketable securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury and agency securities |  | $ | 185,844 |  |  | $ | 145 |  |  | $ | (4 | ) |  | $ | 185,985 |
Commercial paper |  |  | 29,887 |  |  |  | — |  |  |  | — |  |  |  | 29,887 |
Corporate debt securities |  |  | 99,578 |  |  |  | 319 |  |  |  | (5 | ) |  |  | 99,892 |
Total marketable securities |  | $ | 315,309 |  |  | $ | 464 |  |  | $ | (9 | ) |  | $ | 315,764 |
Schedule of Contractual Maturities of Available-for-sale Debt Securities | Contractual maturities of available-for-sale debt securities, as of September 30, 2019, were as follows (in thousands):
|  |  |  |  |  |  |  | Estimated |
|  |  |  |  |  |  |  | Fair Value |
Due within one year |  |  |  |  |  |  |  | $ | 290,813 |
One to two years |  |  |  |  |  |  |  |  | 24,951 |
Total |  |  |  |  |  |  |  | $ | 315,764 |

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- Definition Tabular disclosure of assets, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, by class that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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