Selected Quarterly Financial Data (unaudited) (Details) (USD $)	1 Months Ended		3 Months Ended																12 Months Ended
	Jul. 31, 2014	Feb. 28, 2011	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Selected Quarterly Financial Data Unaudited [Line Items]
Revenue			$ 12		$ 3,904		$ 49,168		$ 17,269		$ 17,274		$ 16,600		$ 16,483		$ 14,514		$ 70,353,483	$ 64,870,919	$ 34,682,111
Operating Expenses:
Research and development	2,200,000	300,000	3,998		5,675		18,990		12,987		13,533		13,501		18,607		12,259		41,649,389	57,898,971	35,670,418
General and administrative			4,201		4,007		7,968		7,501		6,704		6,143		6,211		6,256		23,677,366	25,313,731	15,054,369
Income (loss) from operations			(8,187)		(5,778)		22,210		(3,219)		(2,963)		(3,044)		(8,335)		(4,001)		5,026,728	(18,341,783)	(16,042,676)
Interest, net			164		161		168		85		89		111		126		139
Other			(58)		(58)		(22)		(7)		(28)		(108)		(18)		0		(144,698)	(153,702)	(947,834)
Net income (loss)			$ (8,081)		$ (5,675)		$ 22,356		$ (3,141)		$ (2,902)		$ (3,041)		$ (8,227)		$ (3,862)		$ 5,459,477	$ (18,032,438)	$ (17,291,758)
Basic net income (loss) per share (in dollars per share)			$ (0.19)	[1]	$ (0.14)	[1]	$ 0.54	[1]	$ (0.09)	[1]									$ 0.14	$ (0.50)	$ (0.48)
Diluted net income (loss) per share (in dollars per share)			$ (0.19)	[1]	$ (0.14)	[1]	$ 0.52	[1]	$ (0.09)	[1]									$ 0.13	$ (0.50)	$ (0.48)
Weighted average common shares outstanding - basic (in shares)			41,736,930		41,564,840		41,398,251		36,193,942										40,242,352	36,036,996	35,858,757
Weighted average common shares outstanding - diluted (in shares)			41,736,930		41,564,840		43,196,754		36,193,942										41,758,101	36,036,996	35,858,757
Basic and diluted net loss per share (in dollars per share)											$ (0.08)	[1]	$ (0.08)	[1]	$ (0.23)	[1]	$ (0.11)	[1]
Weighted average common shares outstanding - basic and diluted (in shares)											36,146,061	[2]	36,077,440	[2]	35,991,402	[2]	35,930,265	[2]

[1] Per common share amounts for the quarters and full years have been calculated separately. Accordingly, the sum of quarterly amounts may not equal the annual amount because of differences in the weighted average common shares outstanding during each period, principally due to the effect of share issuances by the Company during the year.

[2] Diluted weighted average common shares outstanding are identical to basic weighted average common shares outstanding and diluted net loss per share is identical to basic net loss per share for all quarters of 2013 because common share equivalents are excluded from the calculations of diluted weighted average common shares outstanding for those quarters, as their effect is anti-dilutive.