Basis of presentation (Details 1) (Level 2 [Member], USD $)	3 Months Ended
	Mar. 31, 2013
Liabilities [Member]
Reconciliation of the beginning and ending balances for the assets and liabilities measured at fair value using observable inputs
Decrease in fair value of warrants	$ (1,046,931)
Warrant liability as of December 31, 2012	4,497,977
Number of warrant liability as of December 31, 2012	2,009,436
Decrease in number of warrants
Warrant liability as of March 31, 2013	3,451,046
Number of warrant liability as of March 31, 2013	2,009,436
Assets [Member]
Reconciliation of the beginning and ending balances for the assets and liabilities measured at fair value using observable inputs
Warrant asset as of December 31, 2012	50,300
Number of warrant assets as of December 31, 2012	2,000,000
Decrease in fair value of warrants	(21,980)
Decrease in number of warrants
Warrant asset as of March 31, 2013	$ 28,320
Number of warrant asset as of March 31, 2013	2,000,000