Subsequent Events (Details) (USD $)	12 Months Ended			98 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended	2 Months Ended		0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Jun. 21, 2012 June 2012 controlled equity sales agreement	Dec. 31, 2012 June 2012 controlled equity sales agreement	Dec. 31, 2013 June 2012 controlled equity sales agreement	Mar. 14, 2014 Subsequent events June 2012 controlled equity sales agreement	Feb. 27, 2014 Subsequent events June 2012 controlled equity sales agreement	Mar. 05, 2014 Subsequent events June 2012 controlled equity sales agreement	Mar. 05, 2014 Subsequent events June 2012 controlled equity sales agreement Maximum
Subsequent events
Common stock sold by the entity (in shares)						815,654	758,093	107,808	3,644,143
Gross proceeds from sale of common stock by the entity	$ 94,734,000	$ 55,862,000	$ 34,369,000	$ 211,168,000		$ 4,111,802	$ 4,700,000	$ 656,238	$ 21,216,860
Common stock, average selling price (in dollars per share)						$ 5.04		$ 6.09	$ 5.82
Maximum share amount to be issued and sold under agreement					30,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001		$ 0.0001						$ 0.0001
Additional aggregate offering price of common stock											$ 50,000,000
Commission payable to Cantor as a percentage of gross sales price per share sold											3.00%