Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

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, 2013, 2012 and 2011 (in thousands):

	Years Ending December 31,
	2013			2012			2011
United States	$	(111,791	)	$	(76,755	)	$	(50,655	)
Foreign		(4,598	)		(6,377	)		(3,306	)
Loss before income taxes	$	(116,389	)	$	(83,132	)	$	(53,961	)

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,
	2013			2012
Net operating loss carry forwards	$	89,491		$	48,591
Capitalized start-up costs		9,406			9,931
Research and development credits		3,896			1,527
Stock compensation		9,390			5,522
Other		4,787			5,028
Total deferred tax assets		116,970			70,599
Valuation allowance		(114,337	)		(69,571	)
Deferred tax liability—fixed assets		(2,633	)		(1,028	)
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, 2013, 2012 and 2011, were as follows:

	Years Ending December 31,
	2013			2012			2011
Federal income tax statutory rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefits		4.1			4.5			6.0
Revalued common and preferred stock warrants		—			0.9			(2.3	)
Revalued derivative liability		(1.8	)		—			—
Incentive stock option compensation		(1.6	)		(1.9	)		(2.4	)
Research tax credits		1.6			—			0.4
Other		1.9			(0.1	)		(0.1	)
Valuation allowance		(38.2	)		(37.4	)		(35.6	)
Effective income tax rate		0.0	%		0.0	%		0.0	%

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, 2010	$	483
Addition based on tax positions related to current year		94
Subtractions based on tax positions related to prior year		(142	)
Balance as of December 31, 2011		435
Addition based on tax positions related to current year		89
Additions based on tax positions related to prior year		95
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