| Business and summary of significant accounting policies - Foreign currency translation (Details) - USD ($) | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2015 | Dec. 31, 2014 | |
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | ||
| Foreign currency transaction losses | $ (189,687) | $ (280,098) | 
| X | ||||||||||
| 
- Definition Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
 | 
| X | ||||||||||
| 
- References No definition available. 
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