Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Components of Loss Before Income Taxes

The components of loss before income taxes are as follows for the years ended December 31, 2015, 2014 and 2013 (in thousands):

	Years Ending December 31,
	2015			2014			2013
United States	$	(138,424	)	$	(159,370	)	$	(111,791	)
Foreign	(3,023		)	(2,771		)	(4,598		)
Loss before income taxes	$	(141,447	)	$	(162,141	)	$	(116,389	)

Tax Effects of Temporary Differences and Carry Forwards on Deferred Tax Assets

The tax effects of temporary differences and carry forwards that give rise to significant portions of the deferred tax assets are as follows (in thousands):

	December 31,
	2015			2014
Net operating loss carry forwards	$	187,169		$	140,185
Capitalized start-up costs	7,475			8,051
Research and development credits	6,320			5,603
Stock compensation	12,683			10,630
Other	6,875			6,634
Total deferred tax assets	220,522			171,103
Valuation allowance	(216,220		)	(166,180		)
Deferred tax liability—fixed assets	(3,056		)	(3,346		)
Deferred tax liability—derivative liability	(1,246		)	(1,577		)
Net deferred tax assets, after valuation allowance	$	—		$	—

Reconciling Items from Income Tax Computed at Statutory Federal Rate

Reconciling items from income tax computed at the statutory federal rate for the years ended December 31, 2015, 2014 and 2013, were as follows:

	Years Ending December 31,
	2015		2014		2013
Federal income tax statutory rate	34.0	%	34.0	%	34.0	%
State income taxes, net of federal benefits	2.2		1.6		4.1
Revalued derivative liability	—		0.6		(1.8	)
Incentive stock option compensation	(0.4	)	(1.3	)	(1.6	)
Research tax credits	0.4		0.8		1.6
Other	(0.1	)	0.3		1.9
Valuation allowance	(36.1	)%	(36.0	)%	(38.2	)%
Effective income tax rate	—	%	—	%	—	%

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

Balance as of December 31, 2012	$	619
Addition based on tax positions related to current year	441
Additions based on tax positions related to prior year	428
Balance as of December 31, 2013	1,488
Addition based on tax positions related to current year	6,411
Additions based on tax positions related to prior year	4,042
Balance as of December 31, 2014	11,941
Addition based on tax positions related to current year	184
Reduction based on tax positions related to prior year	(9,799		)
Additions based on tax positions related to prior year	86
Balance as of December 31, 2015	$	2,412