Stockholders' equity (Public Offerings) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Stockholders' equity [Abstract]
Shares issued during period		11,500,000
Shares issued during period, price per share		$ 1.25
Value of shares issued during period		$ 14,400,000
Cost of shares issued during period		1,405,000
Placement fee percentage		7.00%
Warrants, number of shares per warrant		0.35
Warrants, number of shares		4,025,000
Exercise price of warrants	1.36	1.36
Underwriter, addtional shares purchased		15.00%
Shares issued for warrants exercised	1,161,570
Value of shares issued for warrants exercised	$ 1,580,000