Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

Income Tax Disclosure [Abstract]

Significant Components of Deferred Tax Assets

Significant components of deferred tax assets are as follows:

	December 31,
	2013			2012
	(In thousands)
Deferred tax assets:
Net operating loss carryforwards	$	68,942		$	59,124
Deferred rent	2,770			1,579
Stock-based compensation	3,537			2,183
Research and development tax credits	5,707			3,775
Other	1,866			1,614
Total	82,822			68,275
Less valuation allowance	(82,822		)	(68,275		)
Net deferred tax assets	$	—		$	—

Reconciliation of Federal Statutory Tax Rate to Effective Income Tax

A reconciliation of the Federal statutory tax rate of 34% to our effective income tax rate follows:

	Year ended December 31,
	2013	2012	2011
Statutory tax rate	(34)%	(34)%	(34)%
Permanent difference	3%	2%	1%
Change in valuation allowance	36%	35%	33%
Research and development credit	(5)%	—%	—%
Other	—%	(3)%	—%
Effective tax rate	—%	—%	—%