Quarterly report pursuant to Section 13 or 15(d)

Significant accounting policies (Schedule of Investment Income) (Details)

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Significant accounting policies (Schedule of Investment Income) (Details) - USD ($)
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Interest income $ 49,225 $ 64,550
Realized (losses) (21) (2,893)
Unrealized gains 11,575 29,089
Management fee expenses (8,435) (11,354)
Net investment income $ 52,344 $ 79,392