Summary of significant accounting policies (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net income (loss)	$ 22,006	$ (4,452,305)	$ 2,384,729
Amounts allocated to participating preferred stockholders under the two-class method	(2,507)		(283,154)
Net income (loss) applicable to common stockholders - basic	19,499	(4,452,305)	2,101,575
Net income (loss) applicable to common stockholders - dilutive	$ 19,499	$ (4,452,305)	$ 2,101,575
Denominator:
Weighted average common stock outstanding (basic) (in shares)	52,943,203	52,187,144	49,348,033
Common equivalent shares from options and warrants to purchase common stock	1,522,082		2,819,459
Weighted average common stock outstanding (diluted) (in shares)	54,465,285	52,187,144	52,167,492
Basic net income (loss) per share applicable to common stockholders (in dollars per share)	$ 0.00	$ (0.09)	$ 0.04
Diluted net income (loss) per share applicable to common stockholders (in dollars per share)	$ 0.00	$ (0.09)	$ 0.04
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	9,395,244	17,435,682	8,520,297
Contingently issued restricted shares
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	1,600,000	900,000	900,000
Stock options
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	2,458,471	8,528,816	170,543
Warrants
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	85,629	2,055,722	182,539
Convertible debt
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)			1,316,071
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