Stockholder's equity (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Outstanding, ending balance	32,741,589	32,741,589
Stock options and warrants [Member]
Outstanding, beginning balance	5,447,991	5,597,659
Granted	8,541,000	338,333
Cancelled or expired	(3,167,467)	(488,000)
Exercised
Outstanding, ending balance	10,821,525	5,447,991
Outstanding, Exercisable	7,535,886	4,225,664
Weighted Average Exercise Price Price, Beginning	$ 6.75	$ 6.90
Granted	$ 1.05	$ 4.20
Cancelled or expired	$ (6.12)	$ (7.28)
Exercised
Weighted Average Exercise Price Price, Ending	$ 2.40	$ 6.75
Weighted Average Exercise Price Price, Exercisable	$ 3.00	$ 6.75
Weighted Average Remaining Contractual Term	47 years 4 months 24 days	37 years 10 months 24 days
Weighted Average Remaining Contractual Term, Exercisable	45 years 9 months 18 days	37 years
Aggregate Instrinsic Value
Aggregate Instrinsic Value, Exercisable