Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis

Financial assets and liabilities measured at fair value on a recurring basis are summarized below at December 31, 2015 and 2014 (in thousands):

	Fair Value Measurements at December 31, 2015
	Total		Level 1		Level 2		Level 3
Assets:
Current:
Cash and cash equivalents*	$	18,039	$	—	$	18,039
Commercial paper		24,917		—		24,917		—
Corporate debt securities		86,450		—		86,450		—
Foreign government bonds		6,943		—		6,943		—
Noncurrent:
Corporate debt securities		51,131		—		51,131		—
Foreign government bonds		4,004		—		4,004		—
Total assets measured at fair value	$	191,484	$	—	$	191,484	$	—
Liabilities:
Current:
Warrant derivative liability	$	—	$	—	$	—	$	—
Total liabilities measured at fair value	$	—	$	—	$	—	$	—

*This amount excludes $157.9 million in depository institutions.

	Fair Value Measurements at December 31, 2014
	Total		Level 1		Level 2		Level 3
Assets:
Current:
Cash and cash equivalents*	$	—	$	—	$	—	$	—
Commercial paper
Corporate debt securities		—		—		—		—
Foreign government bonds		—		—		—		—
Noncurrent:
Corporate debt securities		—		—		—		—
Foreign government bonds		—		—		—		—
Total assets measured at fair value	$	—	$	—	$	—	$	—
Liabilities:
Current:
Warrant derivative liability	$	177	$	—	$	—	$	177
Total liabilities measured at fair value	$	177	$	—	$	—	$	177

*This amount excludes $59.1 million in depository institutions.

Schedule of Assumptions Used For Valuing The Warrants

The assumptions used in valuing these warrants are presented in the table below.

	April 30, 2015 (settlement date)			December 31,2014
Expected dividend yield		0	%		0	%
Expected volatility		80.0	%		79.5	%
Risk-free interest rate		1.43	%		1.67	%
Marketability discount		10.0	%		10.0	%

Schedule of Warrant Liability Measured At Fair Value Using Significant Unobservable Input (Level 3)

Activity for the warrant derivative liability measured at fair value using significant unobservable inputs (Level 3) is presented in the table below:

	Warrant Derivative Liability
Balance January 1, 2015	$	177
Adjustment to estimated fair value		1,366
Warrant exercised		(1,543	)
Balance at December 31, 2015	$	—