Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate

A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:

	Year Ended December 31,
	2013			2012			2011
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		4.3			4.5			4.2
Permanent differences		(2.0	)		(0.2	)		(0.4	)
Stock-based compensation		(0.6	)		(0.3	)		(1.2	)
Tax credits		12.4			1.1			3.9
Foreign rate differential		(2.8	)		(4.1	)		(4.4	)
Other		(1.5	)		(0.5	)		(0.8	)
Change in valuation allowance		(44.8	)		(35.5	)		(36.3	)
		—	%		—	%		—	%

Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2013 and 2012 are as follows:

(in thousands)	2013			2012
Deferred tax assets
Net operating losses	$	113,843		$	77,806
Capitalized research and development expenses		32,771			40,083
Credit carryforwards		37,304			14,398
Depreciation		2,735			2,931
Deferred compensation		8,249			5,068
Accrued expenses		841			1,184
Deferred revenue		28,381			29,936
Other temporary differences		5,885			1,934
Total gross deferred tax asset		230,009			173,340
Valuation allowance		(207,304	)		(169,651	)
Net deferred tax asset		22,705			3,689
Deferred tax liabilities
Intangible assets		(3,234	)		(3,689	)
Debt discount		(19,471	)		—
Net deferred taxes	$	—		$	—

Schedule of Changes in the Valuation Allowance

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2013, 2012 and 2011 was as follows:

(in thousands)	Balance at beginning of period		Additions		Deductions		Balance at end of period
December 31, 2011	$	103,881		28,802		—	$	132,683
December 31, 2012	$	132,683		36,968		—	$	169,651
December 31, 2013	$	169,651		37,653		—	$	207,304