Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2016

Fair value, assets measured on recurring basis

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

Fair value, liabilities measured on a recurring basis

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