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Outstanding warrants (Details)
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Dec. 31, 2012
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Oct. 31, 2009
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|---|---|---|
| Class of Warrant or Right [Line Items] | ||
| Outstanding warrants to purchase membership units | 62,280 | |
| Exercise price of warrants | 22.94 | |
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Minimum [Member]
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| Class of Warrant or Right [Line Items] | ||
| Exercise price of warrants | 22.94 | |
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Maximum [Member]
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| Class of Warrant or Right [Line Items] | ||
| Exercise price of warrants | 32.00 |
| X | ||||||||||
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- Definition
Exercise price per share or per unit of warrants or rights outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Details
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| X | ||||||||||
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- Definition
Number of warrants or rights outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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