Quarterly Financial Data (unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
	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
Quarterly Financial Data [Abstract]
Total revenues	$ 100,000	$ 0	$ 0	$ 0	$ 100,000	$ 0	$ 200,000	$ 0
Net income (loss)	$ (13,439,000)	$ (5,625,000)	$ (15,719,000)	$ 4,665,000	$ (27,218,000)	$ (9,980,000)	$ (3,423,000)	$ (6,864,000)	$ (30,117,980)	$ (47,485,437)	$ (17,963,873)
Basic income (loss) per share applicable to common stock	$ (0.24)	$ (0.10)	$ (0.28)	$ 0.09
Diluted income (loss) per share applicable to common stock	$ (0.24)	$ (0.10)	$ (0.28)	$ 0.08
Basic and diluted loss per share applicable to common stock					$ (0.68)	$ (0.33)	$ (0.11)	$ (0.23)	$ (0.55)	$ (1.44)	$ (0.78)