Stockholders' equity (Details 1)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Shares
Outstanding, ending balance	32,741,589	32,741,589
Warrant [Member]
Shares
Outstanding, beginning balance	7,977,990	8,409,531
Warrants issued during the year for consulting and advisory services		338,333
Warrants issued in connection with sales of common and preferred stock	17,918,675	200,000
Warrants expired or cancelled during the year	(1,962,738)	(307,445)
Warrants exercised		(662,429)
Outstanding, ending balance	23,933,927	7,977,990