Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended
	Jul. 31, 2008	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Second Public Offering [Member]	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock authorized for issuance under prior shelf registration statement with SEC, dollar amount						$ 50,000
Common stock, shares authorized		300,000,000	200,000,000
Sales per share price range				$ 3.14
Shares sold	6,686,650	12,600,000		31,846,950
Proceeds from shares sold		$ 34,000		$ 94,700
Common stock issued upon exercise in full over-allotment granted				4,153,950
Sales per share price range	$ 2.68				$ 2.06	$ 3.38