SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Schedule of estimated useful lives of assets

Depreciation of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets, as follows:

Computer equipment	3 years
Office and other equipment	6 years
Laboratory equipment	6 years
Leasehold improvements	The lesser of the lease term or the life of the asset

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

	December 31, 2014		Level 1		Level 2		Level 3
Assets
Cash and cash equivalents	$	6,593	$	4,590	$	2,003	$	—
Short-term investments	22,710		—		22,710		—
	$	29,303	$	4,590	$	24,713	$	—

	December 31, 2013		Level 1		Level 2		Level 3
Assets
Cash and cash equivalents	$	14,235	$	12,431	$	1,804	$	—
Short-term investments	47,835		—		47,835		—
	$	62,070	$	12,431	$	49,639	$	—
Liabilities
Warrant liability	$	33,407	$	—	$	—	$	33,407
	$	33,407	$	—	$	—	$	33,407

Schedule of rollforward of the fair value of the liability which includes Level 3 measurements

The following table presents a rollforward of the fair value of the warrant liability, which included Level 3 measurements (in thousands):

	Fair Value Measurements at Reporting Date Using Significant Unobservable Inputs (Level 3)
Warrant liability:
Balance at January 1, 2013	$	—
Fair value upon reclassification of balance as of January 1, 2013	16,194
Change in fair value of warrant liability included in net loss	19,799
Fair value of warrants exercised	(2,586		)
Balance at December 31, 2013	33,407
Change in fair value of warrant liability included in net loss	4,517
Fair value of warrants exercised	(993		)
Reclassification of warrants to stockholders' equity	(36,931		)
Balance at December 31, 2014	$	—

Schedule of assumptions used to calculate fair value of the liability

The following assumptions were used in the Black-Scholes option-pricing model as of the warrant amendments dates to determine the fair value of the warrants to reclassify into equity:

	September 2014				December 2014
	2011 Warrants		2012 Warrants		2011 Warrants
Risk-free interest rate	1.2	%	1.2	%	1.0	%
Volatility	108.6	%	100.8	%	62.8% - 63.9%
Dividend yield	—		—		—
Expected life in years	1.6		3.2		1.3

The following assumptions were used in the Black-Scholes option-pricing model to determine the fair value of the warrant liability as of December 31, 2013. All 2011 and 2012 warrants were amended and did not require a valuation as of December 31, 2014.

	December 31, 2013
	2011 Warrants		2012 Warrants
Risk-free interest rate	1.2	%	1.6	%
Volatility	112.0	%	115.9	%
Dividend yield	—		—
Expected life in years	2.3		3.9

Schedule of potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive

The following table presents the weighted average number of potentially dilutive securities not included in the calculation of diluted net loss per share due to the anti-dilutive effect of the securities:

	Year ended
	December 31,
	2014	2013	2012
Common stock options	253,595	495	15,663
Common stock warrants	1,515,445	644,426	690,046
Total	1,769,040	644,921	705,709