Stockholders' equity (Public Offerings) (Details) - USD ($)	1 Months Ended	9 Months Ended
	Apr. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stockholders Equity [Line Items]
Shares issued during period	8,335,000
Shares issued during period, price per share	$ 2.40
Value of shares issued during period	$ 20,000,000
Cost of shares issued during period	$ 1,543,000
Placement fee percentage	6.50%
Shares issued for warrants exercised		0	1,161,570
Exercise price of warrants			$ 1.36
Value of shares issued for warrants exercised			$ 1,580,000
Incentive stock options exercised to purchase common shares			39,079
Average exercise price			$ 2.09
Total proceeds from stock options exercised to purchase common shares			$ 82,000
Intrinsic value of stock options exercised to purchase common shares			$ 14,000