Fair Value Measurements

12 Months Ended

Dec. 31, 2017

The tables below present information about the Company's assets that are regularly measured and carried at fair value on a recurring basis at December 31, 2017 and 2016, and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value, which is described further within Note 2, Summary of Significant Accounting Policies.

Financial assets measured at fair value on a recurring basis at December 31, 2017 and 2016 are summarized as follows (in thousands):



Description	Balance as of December 31, 2017		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds	$	49,204	$	49,204	$	—	$	—
Overnight repurchase agreements	11,250		—		11,250		—
Marketable securities:
U.S. government-sponsored enterprise securities	18,181		—		18,181		—
Corporate debt securities	148,874		—		148,874		—
Certificates of deposit	7,794		—		7,794		—
Commercial paper obligations	108,630		—		108,630		—
Asset-backed securities	22,760		—		22,760		—
Total	$	366,693	$	49,204	$	317,489	$	—



Description	Balance as of December 31, 2016		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)
Assets:
Cash equivalents:
Money market funds	$	121,510	$	121,510	$	—	$	—
Overnight repurchase agreements	24,000		—		24,000		—
Marketable securities:
Corporate debt securities	47,906		—		47,906		—
Commercial paper obligations	84,436		—		84,436		—
Asset-backed securities	70,071		—		70,071		—
Total	$	347,923	$	121,510	$	226,413	$	—

As of December 31, 2017, the Company held $11.3 million in overnight repurchase agreements. Overnight purchase agreements yields are comparable to money market funds. Principal and interest on the instruments is due the next day. The instruments are classified as Level 2 due to the collateral including both U.S. government-sponsored enterprise securities and treasury instruments.

There have been no impairments of the Company’s assets measured and carried at fair value during the years ended December 31, 2017 and 2016. In addition, there were no changes in valuation techniques or transfers between Level 1 and Level 2 financial assets during the years ended December 31, 2017 and 2016. The fair value of Level 2 instruments classified as marketable securities was determined through third party pricing services. The carrying amounts reflected in the Company’s consolidated balance sheets for cash, collaboration receivable, other current assets, accounts payable and accrued expenses approximate fair value due to their short-term maturities. The Company did not have any non-recurring fair value measurements on any assets or liabilities at December 31, 2017 and 2016.

- 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.

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