Fair Value Measurements

3 Months Ended

Mar. 31, 2016

We have certain financial assets recorded at fair value which have been classified as Level 1, 2, or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.

Accounting standards define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants as of the measurement date. Market participants are buyers and sellers in the principal market that are (i) independent, (ii) knowledgeable, (iii) able to transact, and (iv) willing to transact. The accounting standards provide an established hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs that market participants would use in valuing the asset or liability and are developed based on market data obtained from independent sources. Unobservable inputs are inputs that reflect our assumptions about the factors that market participants would use in valuing the asset or liability. The accounting standards prioritize the inputs used in measuring the fair value into the following hierarchy:


•	Level 1 includes financial instruments for which quoted market prices for identical instruments are available in active markets.

•

Level 2 includes financial instruments for which there are inputs other than quoted prices included within Level 1 that are observable for the instrument such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets with insufficient volume or infrequent transactions (less active markets) or model-driven valuations in which significant inputs are observable or can be derived principally from, or corroborated by, observable market data.


•	Level 3 includes financial instruments for which fair value is derived from valuation techniques in which one or more significant inputs are unobservable, including management’s own assumptions.

Financial Assets Measured at Fair Value

The following table presents our fair value hierarchy for assets measured at fair value on a recurring basis as of March 31, 2016 and December 31, 2015 (in thousands):



	Fair value as of March 31, 2016
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents	$	17,482	$	17,482	$	—	$	—
Corporate debt securities	70,365		—		70,365		—
Certificates of deposit	11,240		—		11,240		—
Commercial paper	4,244		—		4,244		—
	$	103,331	$	17,482	$	85,849	$	—



	Fair value as of December 31, 2015
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents	$	15,152	$	15,152	$	—	$	—
Corporate debt securities	80,967		—		80,967		—
Certificates of deposit	13,640		—		13,640		—
Commercial paper	3,496		—		3,496		—
	$	113,255	$	15,152	$	98,103	$	—

We obtain pricing information from quoted market prices or quotes from brokers/dealers. We generally determine the fair value of our investment securities using standard observable inputs, including reported trades, broker/dealer quotes, bids and/or offers. Refer to Note 3 for information regarding our investments.

Financial Liabilities Measured at Fair Value

In October 2012, in conjunction with our initial public offering, the amended and restated convertible promissory note originally issued in February 2010 rolled over into a new promissory note (the "Post-IPO GSK Note"). The Post-IPO GSK Note was established in the principal amount of $5.4 million, with a maturity date of October 9, 2015. We used an income approach in the form of a convertible bond valuation model to value our convertible note payable. The convertible bond model considered the debt and option characteristics of the note.

On January 29, 2015, the principal amount outstanding under the Post-IPO GSK Note of $5.4 million was converted into 1,356,738 shares of our common stock at a conversion price of $4.00 per share. A final valuation upon conversion was performed, considering only the option characteristics of the note as its conversion was certain. Key inputs of volatility, risk-free rate and credit spread were considered, however, the final valuation was substantially driven by the number of shares of common stock issued upon conversion (1,356,738) and our stock price on the date of conversion ($18.58). Upon issuance of the common stock, the fair value of the convertible note was classified into stockholders' equity. We recorded a loss from the change in valuation of the convertible note payable of $1.8 million in the condensed statements of operations and comprehensive loss upon conversion in January 2015.

- 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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