Basis of Presentation (Details 2) (USD $)	3 Months Ended								12 Months Ended			98 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2010
Basis of Presentation
Accumulated deficit	$ 171,177,000				$ 109,053,000				$ 171,177,000	$ 109,053,000		$ 171,177,000
Net cash used in operating activities									52,631,000	31,125,000	21,231,000	126,838,000
Cash and cash equivalents	18,130,000				12,416,000				18,130,000	12,416,000	13,245,000	18,130,000	1,707,000
Available-for-sale securities	50,027,000				20,086,000				50,027,000	20,086,000		50,027,000
Net losses from operations	19,357,000	13,474,000	11,858,000	17,622,000	11,532,000	10,088,000	9,545,000	7,070,000	62,311,000	38,235,000	20,164,000	176,760,000
Net cash provided by financing activities									89,230,000	52,088,000	32,636,000	199,356,000
Working capital	$ 56,200,000								$ 56,200,000			$ 56,200,000