Annual report pursuant to Section 13 and 15(d)

Organization and summary of significant accounting policies (Schedule of Investment Income) (Details)

v3.7.0.1
Organization and summary of significant accounting policies (Schedule of Investment Income) (Details) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]    
Interest income $ 126,296 $ 153,586
Realized gains (losses) (3,316) (34,791)
Unrealized gains (losses) 20,641 (7,246)
Management fee expenses (21,897) (29,549)
Net investment income $ 121,724 $ 82,000