Stock-based compensation (Details) (Employee Stock Option [Member], USD $)	6 Months Ended
	Jun. 30, 2014
Employee Stock Option [Member]
Number of shares, Converted outstanding options at January 1, 2014	4,402,890
Number of shares, Granted
Number of shares, Exercised	(477,795)
Number of shares, Cancelled	(76,702)
Number of shares, Outstanding ending balance	3,848,393
Number of shares, Options exercisable ending	3,918,139
Weighted average exercise price, Outstanding beginning balance	$ 0.11
Weighted average exercise price, Granted
Weighted average exercise price, Exercised	$ 0.11
Weighted average exercise price, Cancelled	$ 0.11
Weighted average exercise price, Outstanding ending balance	$ 0.11
Weighted average exercise price, Options exercisable	$ 0.10
Aggregate intrinsic value, Outstanding beginning balance	$ 937,816
Aggregate intrinsic value, Granted
Aggregate intrinsic value, Exercised	(101,293)
Aggregate intrinsic value, Cancelled	(16,107)
Aggregate intrinsic value, Outstanding ending balance	808,163
Aggregate intrinsic value, Options exercisable	$ 861,991