Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2013

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis

The following tables show assets and liabilities measured at fair value on a recurring basis as of December 31, 2013 and 2012 and the input categories associated with those assets and liabilities:

As of December 31, 2013 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents—money market funds	$	47,740	$	—	$	—
Cash equivalents—commercial paper		—		13,998		—
Investments—commercial paper		—		49,680		—
Investments—corporate debt securities		—		40,436		—

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

Schedule of Fair Value of the Liabilities Categorized as Level 3 Instruments

The following table provides a roll-forward of the fair value of the liabilities categorized as Level 3 instruments, for the years ended December 31, 2013 and 2012:

(in thousands)	Convertible preferred stock warrants			Derivative Liability
Balance, December 31, 2011	$	1,516		$	—
Unrealized gain included in other income (expense)		(587	)		—
Reclassification to common stock warrants		(929	)		—
Portion of convertible note allocated to derivative		—			196
Balance, December 31, 2012	$	—		$	196
Portion of convertible note allocated to derivative		—			35
Remeasurement of derivative liability upon conversion of underlying note		—			(231	)
Balance, December 31, 2013	$	—		$	—

Schedule of Quantitative Information Associated with the Fair Value Measurement of the Company's Non-Recurring Level 3 Inputs

The following table provides quantitative information associated with the fair value measurement of the Company’s non-recurring Level 3 inputs:

	Fair Value as of August 31, 2013		Valuation Technique	Unobservable Input	Percentage
	(in thousands)
IPR&D asset	$	—	Income approach—Probability weighted discounted cash flow analysis	Discount rate		25.7	%