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Fair Value Measurements | 3 Months Ended
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Mar. 31, 2018
Fair Value Disclosures [Abstract] |
Fair Value Measurements | Fair Value Measurements We determine the fair values of our financial instruments based on the fair value hierarchy, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value assumes that the transaction to sell the asset or transfer the liability occurs in the principal or most advantageous market for the asset or liability and establishes that the fair value of an asset or liability shall be determined based on the assumptions that market participants would use in pricing the asset or liability. The classification of a financial asset or liability within the hierarchy is based upon the lowest level input that is significant to the fair value measurement. The fair value hierarchy prioritizes the inputs into three levels that may be used to measure fair value: Level 1 - Inputs are unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 - Inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. Level 3 - Inputs are unobservable inputs based on our assumptions. Financial Assets Cash equivalents primarily consist of AAA-rated money market funds with overnight liquidity and no stated maturities. We classified cash equivalents as Level 1 due to the short-term nature of these instruments and measured the fair value based on quoted prices in active markets for identical assets. When available, our marketable securities are valued using quoted prices for identical instruments in active markets. If we are unable to value our marketable securities using quoted prices for identical instruments in active markets, we value our investments using broker reports that utilize quoted market prices for comparable instruments. We validate, on a sample basis, the derived prices provided by the brokers by comparing their assessment of the fair values of our investments against the fair values of the portfolio balances of another third-party professional pricing service. As of March 31, 2018, all of our marketable securities were valued using quoted prices for comparable instruments in active markets and are classified as Level 2. Based on our valuation of our money market funds and marketable securities, we concluded that they are classified in either Level 1 or Level 2 and we have no financial assets measured using Level 3 inputs. The following table presents information about our assets that are measured at fair value on a recurring basis using the above input categories (in thousands):
|  | Fair Value Measurements as of March 31, 2018 |  | Fair Value Measurements as of December 31, 2017
Description |  | Total |  | Level 1 |  | Level 2 |  | Total |  | Level 1 |  | Level 2
Money market funds |  | $ | 54,830 |  | $ | 54,830 |  | $ | — |  | $ | 49,452 |  | $ | 49,452 |  | $ | —
U.S. treasury debt securities |  | 3,080 |  | — |  | 3,080 |  | 3,075 |  | — |  | 3,075
U.S. corporate debt securities |  | 12,721 |  | — |  | 12,721 |  | 13,289 |  | — |  | 13,289
|  | $ | 70,631 |  | $ | 54,830 |  | $ | 15,801 |  | $ | 65,816 |  | $ | 49,452 |  | $ | 16,364
Included in cash and cash equivalents |  | $ | 54,830 |  |  |  |  |  | $ | 49,452 |  |  |  |
Included in marketable securities |  | $ | 15,801 |  |  |  |  |  | $ | 16,364 |  |  |  |

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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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