Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 53,865,380	$ 40,182,141
Prepaid expenses	495,221us-gaap_PrepaidExpenseCurrent	803,775us-gaap_PrepaidExpenseCurrent
Total current assets	54,360,601us-gaap_AssetsCurrent	40,985,916us-gaap_AssetsCurrent
Property and equipment, net of accumulated depreciation of $290,669 in 2015 and $285,643 in 2014	12,229,840us-gaap_PropertyPlantAndEquipmentNet	12,046,267us-gaap_PropertyPlantAndEquipmentNet
Prepaid expenses, long-term	1,677,434us-gaap_PrepaidExpenseNoncurrent	1,677,434us-gaap_PrepaidExpenseNoncurrent
Deferred financing costs, net	410,069	98,401
Other assets	18,208us-gaap_OtherAssetsNoncurrent	18,208us-gaap_OtherAssetsNoncurrent
Total assets	68,696,152us-gaap_Assets	54,826,226us-gaap_Assets
Current liabilities:
Accounts payable	3,309,188us-gaap_AccountsPayableCurrent	2,631,217us-gaap_AccountsPayableCurrent
Accrued expenses	1,108,412us-gaap_AccruedLiabilitiesCurrent	1,062,113us-gaap_AccruedLiabilitiesCurrent
Loan payable, current portion		5,003,143us-gaap_LoansPayableCurrent
Warrant liability	396,892us-gaap_DerivativeLiabilitiesCurrent	296,048us-gaap_DerivativeLiabilitiesCurrent
Total current liabilities	4,814,492us-gaap_LiabilitiesCurrent	8,992,521us-gaap_LiabilitiesCurrent
Loan payable, long-term	15,124,990us-gaap_LongTermLoansPayable	9,827,758us-gaap_LongTermLoansPayable
Commitment and contingencies
Stockholders' equity:
Common stock, $.0001 par value, authorized 150,000,000 shares; 22,160,233 shares issued and outstanding as of March 31, 2015 and 18,634,872 shares issued and outstanding as of December 31, 2014	2,217us-gaap_CommonStockValue	1,864us-gaap_CommonStockValue
Additional paid-in capital	191,684,665us-gaap_AdditionalPaidInCapital	170,395,934us-gaap_AdditionalPaidInCapital
Accumulated deficit	(142,930,212)	(134,391,851)
Total stockholders' equity	48,756,670us-gaap_StockholdersEquity	36,005,947us-gaap_StockholdersEquity
Total liabilities and stockholders' equity	$ 68,696,152	$ 54,826,226

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph a

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682