INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2015

INCOME TAXES

Schedule of components of the net deferred tax asset

The components of the net deferred tax asset with the approximate income tax effect of each type of carryforward, credit and temporary differences are as follows. Amounts included in the table are in thousands.

	December 31,
	2015		2014
Deferred tax assets:
Operating loss carryforwards	$	189,007	$	140,471
Tax credit carryforwards		17,947		16,915
Deferred revenue		—		11
Other temporary differences		8,146		4,543
Tax assets before valuation allowance		215,100		161,940
Less—Valuation allowance		(215,100)		(161,940)
Net deferred taxes	$	—	$	—

Schedule of differences between the effective income tax rate and the statutory tax rate

	December 31,
	2015		2014		2013
U.S. Federal statutory rate	35.0	%	34.0	%	34.0	%
State taxes	2.1		5.5		4.8
Federal and state tax rate changes	(1.7)		—		—
Research and development tax credits	0.9		(1.1)		16.9
Stock-based compensation expense	(0.6)		(0.5)		(1.1)
Other adjustments	(0.9)		(0.8)		(0.3)
Valuation allowance	(34.8)		(37.1)		(54.3)
Effective tax rate	0.0	%	0.0	%	0.0	%