Liquidity (Details) (USD $)	3 Months Ended	6 Months Ended					0 Months Ended	3 Months Ended		6 Months Ended	1 Months Ended					0 Months Ended				0 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 13, 2013 Class A Common Stock Warrants Issued, March 2013	Aug. 06, 2013 At the Market Sales Agreement Common Stock Subsequent event	Jun. 30, 2013 At the Market Sales Agreement Class A Common Stock	Mar. 31, 2013 At the Market Sales Agreement Class A Common Stock	Jun. 30, 2013 At the Market Sales Agreement Class A Common Stock	Jun. 30, 2013 At the Market Sales Agreement Class A Common Stock Subsequent event	Jun. 30, 2013 At the Market Sales Agreement Class A Common Stock Average	Jun. 30, 2013 At the Market Sales Agreement Class A Common Stock Average Subsequent event	Aug. 06, 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	Jul. 25, 2013 Shelf Registration Class A Common Stock Subsequent event	Jul. 25, 2013 Shelf Registration Class A Common Stock Warrants - July 2013 financing - Subscribers Subsequent event	Apr. 23, 2013 Shelf Registration Class A Common Stock Warrants - April 2013 financing - Subscribers	Mar. 13, 2013 Equity issuance Class A Common Stock
Liquidity
Accumulated deficit	$ 410,620,268	$ 410,620,268		$ 396,916,216
Negative working capital	8,303,967	8,303,967
Cash on hand	922,299	922,299	1,570,573	2,112,769	3,385,035
Liquidity
Shelf registration statement, amount															30,000,000
Number of shares sold							3,700,000	840,581	94,988	935,569	807,913					1,585,000	1,204,470			301,205
Share price (in dollars per share)												$ 1.81	$ 1.40			$ 2.00	$ 1.27			$ 3.32
Gross proceeds from issuance of common stock																3,170,000	1,529,677			1,000,000
Placement agent fees equal to gross proceeds from offering (as a percent)																6.00%	6.00%			6.00%
Net proceeds from issuance of common stock		5,473,428	5,143,876				11,800,000	1,380,682	262,945	1,644,000	1,098,000					2,920,000	1,408,000			910,000
Offering costs							380,000	45,000	8,700	54,000	36,000
Placement agent fees																190,200	92,000			60,000
Legal and other fees																60,000	30,000			30,000
Common stock agreed to be issued against warrants (in shares)						150,603												72,268	792,500
Exercise price of warrants (in dollars per share)						$ 3.32												$ 1.27	$ 2.48
Liquidated damages paid to subscribers for failure to file registration statement with SEC	40,000
Gross proceeds available under the shelf registration statement														$ 1,748,000