INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Analysis of Deferred Tax Assets

An analysis of the deferred tax assets is as follows: 

	As of December 31,
	2015			2014
	(in thousands)
Net operating loss carryforwards	$	138,786		$	115,699
Difference in depreciation and amortization		2,694			2,800
Research and development tax credits		31,397			29,127
Stock-based compensation		20,774			13,637
Deferred rent		2,771			2,864
Deferred revenue		1,324			1,213
Capitalized inventory		19,018			—
Other		3,060			413
Gross deferred tax assets		219,824			165,753
Valuation allowance		(219,824	)		(165,753	)
Net deferred tax assets	$	—		$	—

Reconciliation Between Effective Tax Rate and Income Tax Rate

The reconciliation between the Company’s effective tax rate and the income tax rate is as follows:

	For the Year Ended December 31,
	2015				2014				2013
Federal income tax rate		34.0		%		34.0		%		34.0		%
Research and development tax credits		0.3				2.4				1.4
Valuation allowance		(19.1	)			(21.6	)			(12.4	)
Permanent Differences		(1.7	)			(2.4	)			(8.8	)
Foreign rate differential		(13.5	)			(12.4	)			(14.2	)
Effective tax rate		—		%		—		%		—		%

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

The reconciliation of the beginning and ending amount of total unrecognized tax benefits for the years ended December 31, 2015, 2014 and 2013 are as follows:

	For the Year Ended December 31,
	2015		2014		2013
	(in thousands)
Balance at beginning of the period	$	—	$	—	$	—
Increase related to current year tax positions		613		—		—
Increase related to prior year tax positions		3,093		—		—
Balance at end of the period	$	3,706	$	—	$	—