Stockholders' Equity (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended		12 Months Ended
	Jul. 31, 2008	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Second Public Offering [Member]	Dec. 31, 2013 2012 Sales Agreement [Member]	Dec. 31, 2013 Minimum [Member] 2012 Sales Agreement [Member]	Dec. 31, 2013 Maximum [Member] 2012 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock authorized for issuance under prior shelf registration statement with SEC, dollar amount								$ 50,000,000
Common stock, shares authorized		300,000,000	200,000,000
Sales per share price range					$ 3.14		$ 2.06	$ 3.38
Available proceeds						15,000,000
Shares sold	6,686,650				31,846,950	12,600,000
Proceeds from shares sold		$ 170,590,000	$ 53,155,000	$ 11,827,000	$ 95,000,000	$ 34,000,000
Common stock issued upon exercise in full over-allotment granted					4,153,950