Summary of significant accounting policies (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net (loss) income	$ (4,452,305)	$ 2,384,729	$ (3,064,787)
Amounts allocated to participating preferred stockholders under the two-class method		(283,154)
Net (loss) income applicable to common stockholders - basic	(4,452,305)	2,101,575	(3,064,787)
Net (loss) income applicable to common stockholders - dilutive	$ (4,452,305)	$ 2,101,575	$ (3,064,787)
Denominator:
Weighted average common stock outstanding (basic) (in shares)	52,187,144	49,348,033	40,431,073
Common equivalent shares from options and warrants to purchase common stock		2,819,459
Weighted average common stock outstanding (diluted) (in shares)	52,187,144	52,167,492	40,431,073
Basic net (loss) income per share applicable to common stockholders (in dollars per share)	$ (0.09)	$ 0.04	$ (0.08)
Diluted net (loss) income per share applicable to common stockholders (in dollars per share)	$ (0.09)	$ 0.04	$ (0.08)
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	17,435,682	8,520,297	21,826,207
Contingently issued restricted shares
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	915,000	915,000
Stock options
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	8,528,816	170,543	7,264,204
Warrants
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	2,055,722	182,539	3,661,083
Convertible debt
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)		1,316,071	4,049,776
Convertible preferred stock
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	6,851,144	6,851,144	6,851,144