Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2014

Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis

The following table presents our fair value hierarchy for assets and liabilities measured at fair value on a recurring basis at September 30, 2014 and December 31, 2013 (in thousands):

	Fair value as of September 30, 2014
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents	$	8,760	$	8,760	$	—	$	—
Corporate debt securities		68,237		—		68,237		—
Certificates of deposit		13,870		—		13,870		—
Commercial paper		2,000		—		2,000		—
	$	92,867	$	8,760	$	84,107	$	—
Liabilities:
Convertible note payable	$	10,665	$	—	$	—	$	10,665
	Fair value as of December 31, 2013
	Total		Level 1		Level 2		Level 3
Assets:
Cash equivalents	$	17,170	$	17,170	$	—	$	—
Corporate debt securities		71,416		—		71,416		—
Certificates of deposit		11,710		—		11,710		—
Debt securities of U.S. government-sponsored agencies		7,001		—		7,001		—
Commercial paper		6,071		—		6,071		—
	$	113,368	$	17,170	$	96,198	$	—
Liabilities:
Convertible note payable	$	11,279	$	—	$	—	$	11,279

Changes in Estimated Fair Value of Convertible Note Payable

Changes in the estimated fair value of convertible note payable from December 31, 2013 through September 30, 2014 are as follows (in thousands):

	Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Balance at December 31, 2013	$	11,279
Change in estimated fair value of convertible note payable		(614	)
Balance at September 30, 2014	$	10,665