Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2013

Schedule of assets and liabilities measured at fair value on a recurring basis

As of December 31, 2012 (in thousands)	Level 1		Level 2		Level 3

Assets:
Cash equivalents — money market funds	$	25,668	$	—	$	—
Cash equivalents — certificates of deposit	—		480		—
Cash equivalents — corporate debt securities	—		5,017		—
Investments — certificates of deposit	—		240		—
Investments — commercial paper	—		12,465		—
Investments — corporate debt securities	—		59,533		—
Liabilities:
Derivative liability	—		—		196

As of March 31, 2013 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents — money market funds	$	13,667	$	—	$	—
Investments — certificates of deposit	—		240		—
Investments — commercial paper	—		14,483		—
Investments — corporate debt securities	—		43,529		—
Liabilities:
Derivative liability	—		—		231

Schedule of quantitative information associated with the fair value measurement of the Company's Level 3 inputs

	Fair Value as of March 31, 2013		Valuation Technique	Unobservable Input	Point Estimate
	(in thousands)
Derivative Liability	$	231	Probability-weighted	Estimated probability of Silver Creek qualified financing(s) prior to December 31, 2013	50	%

Schedule of fair value of the derivative liability categorized as Level 3 instruments

(in thousands)	Derivative Liability

Balance, December 31, 2012	$	196
Portion of convertible notes issued in February 2013 allocated to derivative	35

Balance, March 31, 2013	$	231

- Definition

Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and gains or losses recognized in other comprehensive income (loss) and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs) by class of liability.

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