Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net operating losses
NOL carryforwards expiring unutilized	$ 800,000
Minimum percentage point aggregate change in ownership, annual limitation	50.00%
Deferred tax assets
Net operating losses	38,131,000	22,809,000
Research & development credits	4,771,000	3,711,000
Start-up expenditures	5,661,000	6,108,000
Stock compensation	518,000	198,000
Depreciation	237,000	79,000
Accruals	129,000	96,000
Deferred revenue		1,533,000
Valuation allowance	(49,447,000)	(34,534,000)
Components of net income tax benefit
Deferred	14,913,000	4,840,000	6,536,000
Valuation allowance	(14,913,000)	(4,840,000)	(6,536,000)
Reconciliation of difference between for income taxes and income taxes at statutory U.S. federal income tax rate
Income tax benefit at statutory rate	12,512,000	3,791,000	5,451,000
State income taxes	1,980,000	595,000	935,000
Research & development credits	542,000	2,926,000
Return to provision adjustments	(475,000)	(36,000)	(3,000)
Permanent items	(596,000)	(324,000)	(2,000)
Federal benefit of prior year state deferred items		(2,112,000)	155,000
Valuation allowance	(14,913,000)	(4,840,000)	(6,536,000)
Reconciliation of the total gross amounts of unrecognized tax benefits
Balance, at beginning of period	655,000
Additions based on tax positions related to current year	187,000	655,000
Balance, at end of period	842,000	655,000
Federal
Net operating losses
Net operating loss carryforwards	$ 96,000,000