| Contingencies and commitments - ThermoFisher License Agreement (Details) | 12 Months Ended | 
|---|---|
| Dec. 31, 2012  USD ($) | |
| License agreement | ThermoFisher | |
| Contingencies and commitments | |
| Upfront license fees | $ 1,000,000 | 
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- Definition Represents the amount of upfront license fees paid. No definition available. 
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| X | ||||||||||
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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| X | ||||||||||
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- Details 
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- Details 
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