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Fair Value Measurements | 12 Months Ended
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Dec. 31, 2017
Fair Value Disclosures [Abstract] |
Fair Value Measurements | 4. Fair Value Measurements The Company’s investments include cash equivalents and available-for-sale investment securities consisting of a money market fund, U.S. Treasury notes, and high quality, marketable debt instruments of corporations and government sponsored enterprises in accordance with the Company’s investment policy. The Company’s investment policy defines allowable investments and establishes guidelines relating to credit quality, diversification, and maturities of its investments to preserve principal and maintain liquidity. All investment securities have a credit rating of at least A3/A- or better, or P-1/A-1 or better, as determined by Moody’s Investors Service or Standard & Poor’s. The Company’s cash equivalents and available-for-sale investment securities are classified within the fair value hierarchy as defined by authoritative guidance. The Company’s investment securities classified as Level 1 are valued using quoted market prices. The Company obtains the fair value of its Level 2 financial instruments from third-party pricing services. The pricing services utilize industry standard valuation models whereby all significant inputs, including benchmark yields, reported trades, broker/dealer quotes, issuer spreads, bids, offers, or other market-related data, are observable. The Company validates the prices provided by the third-party pricing services by reviewing their pricing methods and matrices, and obtaining market values from other pricing sources. After completing the validation procedures, the Company did not adjust or override any fair value measurements provided by these pricing services as of December 31, 2017 and 2016, respectively. The Company does not hold any securities classified as Level 3, which are securities valued using unobservable inputs. The Company has not transferred any investment securities between the classification levels. The recurring fair value measurements of the Company’s cash equivalents and available-for-sale investment securities at December 31, 2017 and 2016 consisted of the following (in thousands):
|  |  |  |  |  | Fair Value Measurements at Reporting Date Using |
|  | December 31, 2017 |  |  | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  | Significant Other Observable Inputs (Level 2) |  |  | Significant Unobservable Inputs (Level 3) |
Money market fund |  | $ | 38,057 |  |  | $ | 38,057 |  |  | $ | — |  |  | $ | — |
U.S. Treasury notes |  |  | 32,964 |  |  |  | 32,964 |  |  |  | — |  |  |  | — |
Government sponsored enterprise securities |  |  | 10,072 |  |  |  | — |  |  |  | 10,072 |  |  |  | — |
Corporate debt securities |  |  | 154,396 |  |  |  | — |  |  |  | 154,396 |  |  |  | — |
Commercial paper |  |  | 98,052 |  |  |  | — |  |  |  | 98,052 |  |  |  | — |
|  | $ | 333,541 |  |  | $ | 71,021 |  |  | $ | 262,520 |  |  | $ | — |
|  |  |  |  |  | Fair Value Measurements at Reporting Date Using |
|  | December 31, 2016 |  |  | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  | Significant Other Observable Inputs (Level 2) |  |  | Significant Unobservable Inputs (Level 3) |
Money market fund |  | $ | 129,292 |  |  | $ | 129,292 |  |  | $ | — |  |  | $ | — |
U.S. Treasury notes |  |  | 82,487 |  |  |  | 82,487 |  |  |  | — |  |  |  | — |
Government sponsored enterprise securities |  |  | 88,773 |  |  |  | — |  |  |  | 88,773 |  |  |  | — |
Corporate debt securities |  |  | 82,857 |  |  |  | — |  |  |  | 82,857 |  |  |  | — |
Commercial paper |  |  | 140,024 |  |  |  | — |  |  |  | 140,024 |  |  |  | — |
|  | $ | 523,433 |  |  | $ | 211,779 |  |  | $ | 311,654 |  |  | $ | — |

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- Definition The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -URI http://asc.fasb.org/topic&trid=2155941 + Details
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