Fair Value Measurement

3 Months Ended

Mar. 31, 2016

Cash Equivalents and Investments

The Company measures the fair value of money market funds and investments based on quoted prices in active markets for identical assets or liabilities. All other financial instruments were valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The Company did not hold any cash equivalents or investments categorized as Level 3 as of March 31, 2016.

The following table summarizes, by major security type, the Company's cash equivalents and investments that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy (in thousands):



	Total Estimated Fair Value as of
	March 31, 2016				December 31, 2015
	Cash Equivalents		Investments		Cash Equivalents		Investments
Level 1 Securities:
Money market funds	$	17,929	$	—	$	24,577	$	—
Level 2 Securities:
Agency securities	—		16,882		—		19,623
Corporate debt securities	540		22,508		850		26,270
US Government securities	—		6,539		—		5,531
Commercial Paper	8,322		2,523		—		499
Total cash equivalents and investments	$	26,791	$	48,452	$	25,427	$	51,923

Convertible Senior Notes

As of March 31, 2016, the fair value of the convertible senior notes, which was determined based on inputs that are observable in the market or that could be derived from, or corroborated with, observable market data, including our stock price, interest rates and credit spread (Level 2) were as follows (in thousands):



	Total Estimated Fair Value as of
	March 31, 2016		December 31, 2015
Convertible senior notes	$	281,589	$	270,192

The carrying value of other financial instruments, including accounts receivable, accounts payable and other payables, approximates fair value due to their short maturities.

- 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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