Basis of presentation (Tables)

3 Months Ended

Mar. 31, 2013

Basis of presentation [Abstract]

Summary of assets and liabilities measured at fair value on a recurring basis

The following table summarizes assets and liabilities measured at fair value on a recurring basis at March 31, 2013 and December 31, 2012, respectively:

	March 31, 2013								December 31, 2012
	Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Fair Value Measurements Using:
Assets
Derivative asset (warrant)	$	—	$	28,320	$	—	$	28,320	$	—	$	50,300	$	—	$	50,300
Liabilities
Derivative liabilities	$	—	$	3,451,046	$	—	$	3,451,046	$	—	$	4,497,977	$	—	$	4,497,977

Reconciliation of the beginning and ending balances for the assets and liabilities measured at fair value using observable inputs

The table below provides a reconciliation of the beginning and ending balances for the assets and liabilities measured at fair value using observable inputs (Level 2). The table reflects net gains and losses for all financial assets and liabilities categorized as Level 2 as of March 31, 2013 and December 31, 2012.

	$			Number of Warrants
Assets:
Warrant asset as of December 31, 2012	$	50,300			2,000,000
Decrease in fair value of warrants		(21,980	)		—
Warrant asset as of March 31, 2013	$	28,320			2,000,000
Liabilities:
Warrant liability as of December 31, 2012	$	4,497,977			2,009,436
Decrease in fair value of warrants		(1,046,931	)		—
Warrant liability as of March 31, 2013	$	3,451,046			2,009,436