Income Taxes (Tables)

12 Months Ended

Dec. 31, 2012

Components of Loss before Income Taxes

The components of loss before income taxes are as follows for the years ended December 31, 2012, 2011 and 2010 (in thousands):

	Years Ending December 31,
	2012			2011			2010
United States	$	(76,755	)	$	(50,655	)	$	(16,420	)
Foreign		(6,377	)		(3,306	)		—
Loss before income taxes	$	(83,132	)	$	(53,961	)	$	(16,420	)

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,
	2012			2011
Net operating loss carry forwards	$	48,591		$	21,850
Capitalized start-up costs		9,931			9,189
Research and development credits		1,527			1,088
Stock compensation		5,522			3,314
Other		5,028			3,597
Total deferred tax assets		70,599			39,038
Valuation allowance		(69,571	)		(38,625	)
Deferred tax liability—fixed assets		(1,028	)		(413	)
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, 2012, 2011 and 2010, were as follows:

	Years Ending December 31,
	2012			2011			2010
Federal income tax statutory rate		34.0	%		34.0	%		34.0	%
State income taxes, net of federal benefits		4.5			6.0			5.8
Revalued preferred stock warrants		0.9			(2.3	)		(6.5	)
Incentive stock option compensation		(1.9	)		(2.4	)		(1.1	)
Research tax credits		—			0.4			3.4
Other		(0.1	)		(0.1	)		(0.2	)
Valuation allowance		(37.4	)		(35.6	)		(35.4	)
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 January 1, 2010	$	265
Addition based on tax positions related to current year		218
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