Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

Income Taxes

Schedule of reconciliation of the statutory U.S. federal rate to the Company's effective tax rate

	Years ended December 31,
	2013			2012			2011
Percent of pre-tax income:
U.S. federal staturtory income tax rate		35.0	%		35.0	%		35.0	%
State taxes, net of federal benefit		—			—			3.4	%
Permanent items		(2.2	)%		(1.0	)%		(0.6	)%
Research and development credit		2.7	%		1.0	%		0.7	%
Change in valuation allowance		(35.5	)%		(35.0	)%		(33.3	)%
Effective income tax rate		—			—			5.2	%

Schedule of significant components of the Company's deferred tax assets/liabilities

	December 31,
	2013			2012
Deferred tax assets/(liabilities)
Federal net operating loss carryforwards	$	30,084		$	29,464
State and local net operating loss carryforwards		5,026			4,825
License and technology payments		6,407			5,566
Share-based compensation		1,396			476
Depreciation		(7	)		(11	)
Federal research and development credit carryforwards		2,966			1,562
State research and development credit carryforwards		1,483			781
Deferred income tax assets		47,355			42,663
Valuation allowance		(47,355	)		(42,663	)
Net deferred tax assets (liabilities)		—			—

Summary of carryforwards of net operating losses and tax credits

The following table summarizes carryforwards of net operating losses and tax credits as of December 31, 2013:

	Amount		Expiration
Federal net operating losses	$	85,955		2033
Research and development credits	$	2,966		2033