Stock incentive plan and stock-based compensation (Details 1) - Warrant [Member] - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of warrants - Warrants outstanding	1,020,825	920,825
Number of warrants - Issued	2,800,000	100,000
Number of warrants - Exercised
Number of warrants - Expired
Number of warrants - Warrants outstanding	3,820,825	1,020,825
Weighted average exercise price - Warrants outstanding	$ 3.47	$ 3.44
Weighted average exercise price - Issued	$ 0.25
Weighted average exercise price - Exercised		$ 3.75
Weighted average exercise price - Expired
Weighted average exercise price - Warrants outstanding	$ 1.11	$ 3.47