Liquidity (Details) (USD $)	3 Months Ended					0 Months Ended	3 Months Ended		0 Months Ended					0 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 13, 2013 Class A Common Stock Warrants Issued, March 2013	May 10, 2013 At the Market Sales Agreement Common Stock Subsequent event	Mar. 31, 2013 At the Market Sales Agreement Class A Common Stock	Mar. 31, 2012 At the Market Sales Agreement Class A Common Stock	Mar. 31, 2013 At the Market Sales Agreement Class A Common Stock Subsequent event	Mar. 31, 2013 At the Market Sales Agreement Class A Common Stock Average	Mar. 31, 2013 At the Market Sales Agreement Class A Common Stock Average Subsequent event	May 10, 2013 Shelf Registration Common Stock Funding plan	Jun. 21, 2011 Shelf Registration Common Stock Funding plan	Apr. 23, 2013 Shelf Registration Class A Common Stock Subsequent event	Apr. 23, 2013 Shelf Registration Class A Common Stock Warrants - April 2013 financing - Subscribers Subsequent event	Mar. 13, 2013 Equity issuance Class A Common Stock
Liquidity
Accumulated deficit	$ 407,129,971		$ 396,916,216
Negative working capital	9,797,084
Cash on hand	1,823,136	2,255,835	2,112,769	3,385,035
Liquidity
Shelf registration statement, amount													30,000,000
Number of shares sold						8,300,000	379,950	1,114,241	32,133					6,340,000		1,204,820
Share price (in dollars per share)										$ 0.72	$ 0.67			$ 0.50		$ 0.83
Gross proceeds from issuance of common stock														3,170,000		1,000,000
Placement agent fees equal to gross proceeds from offering (as a percent)														6.00%		6.00%
Net proceeds from issuance of common stock	1,172,946	2,359,382				9,300,000	262,945	2,359,382	20,800					2,920,000		910,000
Offering costs						299,000	8,700	75,000	800
Placement agent fees														190,200		60,000
Legal and other fees														60,000		30,000
Common stock agreed to be issued against warrants (in shares)					602,410										3,170,000
Exercise price of warrants (in dollars per share)					$ 0.83										$ 0.62
Gross proceeds available under the shelf registration statement												$ 5,816,000