Warrants (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Additional information
Closing stock price as reported on NASDAQ /AIM (in dollars per share)	$ 3.48	$ 2.27	$ 1.35
Warrants
Number of warrants
Outstanding at the beginning of the period (in shares)	2,108,575
Warrants exercised (number of warrants)	(917,602)
Warrants cancelled (number of warrants)	(464,115)
Outstanding at the end of the period (in shares)	726,858	2,108,575
Warrants exercisable at the end of the period (in shares)	726,858
Vested and expected to vest at the end of the period (in shares)	726,858
Weighted-average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 1.65
Warrants exercised (in dollars per share)	$ 1.31
Warrants cancelled (in dollars per share)	$ 1.31
Outstanding at the end of the period (in dollars per share)	$ 2.29	$ 1.65
Warrants exercisable at the end of the period (in dollars per share)	$ 2.29
Vested and expected to vest at the end of the period (in dollars per share)	$ 2.29
Weighted-average remaining contractual life (years)
Outstanding at the end of the period	1 year 3 months 4 days	2 years 10 months 24 days
Warrants exercisable at the end of the period	1 year 3 months 4 days
Vested and expected to vest at the end of the period	1 year 3 months 4 days
Aggregate intrinsic value
Outstanding at the end of the period (in dollars)	$ 1,236,845	$ 1,956,140
Exercisable at the end of the period (in dollars)	1,236,845
Vested and expected to vest at the end of the period (in dollars)	1,236,845
Additional information
Weighted average grant date fair value for warrants granted during the period (in dollars per share)		$ 2.83	$ 1.41
Total fair value of warrants vested during the period (in dollars)		11,254	33,776
Total intrinsic value of warrants exercised during the period (in dollars)	$ 2,376,589	$ 26,975	$ 77,795
Warrants exercised (in shares)	917,602
Number of shares subject to warrant that were cancelled	464,115
Warrants | Minimum
Weighted-average exercise price
Warrants exercisable at the end of the period (in dollars per share)	$ 0.25
Warrants | Maximum
Weighted-average exercise price
Warrants exercisable at the end of the period (in dollars per share)	$ 5.50