Net income per share (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income	$ 371,916	$ 787,147
Amounts allocated to participating preferred stockholders under the two-class method	(42,722)	(93,406)
Net income applicable to common stockholders - basic	329,194	693,741
Net income applicable to common stockholders - diluted	$ 329,194	$ 693,741
Denominator:
Weighted average common stock outstanding (basic) (in shares)	52,779,130	51,782,902
Common equivalent shares from options and warrants to purchase common stock	2,026,896	2,476,598
Weighted average common stock outstanding (diluted) (in shares)	54,806,026	54,259,500
Basic net income per share applicable to common stockholders (in dollars per share)	$ 0.01	$ 0.01
Diluted net income per share applicable to common stockholders (in dollars per share)	$ 0.01	$ 0.01
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	8,559,665	8,815,088
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)	1,544,580	1,781,405
Warrants
Anti-dilutive securities excluded from computation of diluted earnings per share
Total anti-dilutive securities (in shares)	163,941	182,539
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