Common Stock Warrant Liability (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	0 Months Ended		0 Months Ended		0 Months Ended
	Mar. 31, 2013	May 13, 2009 Five Year Warrant 1 [Member]	Mar. 31, 2013 Five Year Warrant 1 [Member]	Feb. 23, 2010 Five Year Warrant 2 [Member]	Mar. 31, 2013 Five Year Warrant 2 [Member]	Feb. 22, 2011 Five Year Warrant 3 [Member]	Mar. 31, 2013 Five Year Warrant 3 [Member]
Class of Warrant or Right [Line Items]
Exercisable period of warrants	5 years	5 years		5 years		5 years
Estimated fair value of warrants accounted for as derivative liabilities [Abstract]
Issuance Date		May 13, 2009		Feb. 23, 2010		Feb. 22, 2011
Number of Warrant Shares Issuable (in shares)		466,667		916,669		4,948,750
Exercise Price (in dollars per share)		$ 17.25		$ 12.75		$ 2.80
Warrant Expiration Date		May 13, 2014		Feb. 23, 2015		Feb. 22, 2016
Fair Value of Warrants		$ 3,360	$ 0	$ 5,701	$ 33	$ 8,004	$ 6,110