Fair value of financial instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative warrant - liability	$ 5,044	$ 7,166
Derivative Liability, Fair Value, Gross Liability	5,044	7,166
Fair Value, Inputs, Level 1 [Member]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 2 [Member]
Derivative Liability, Fair Value, Gross Liability	0	0
Fair Value, Inputs, Level 3 [Member]
Derivative Liability, Fair Value, Gross Liability	$ 5,044	$ 7,166

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, and which are expected to be extinguished or otherwise disposed of after one year or beyond the normal operating cycle, if longer, net of the effects of master netting arrangements.

+ References

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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+ Details