Quarterly report pursuant to Section 13 or 15(d)

Significant accounting policies (Schedule of Trading Securities) (Details)

v3.7.0.1
Significant accounting policies (Schedule of Trading Securities) (Details)
Dec. 31, 2016
USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]  
Trading securities cost, current $ 7,516,404
Trading securities fair value, current 7,506,761
Certificates of deposit / commercial paper [Member]  
Schedule of Trading Securities and Other Trading Assets [Line Items]  
Trading securities cost, current 2,378,222
Trading securities fair value, current 2,373,891
Corporate Bonds [Member]  
Schedule of Trading Securities and Other Trading Assets [Line Items]  
Trading securities cost, current 5,138,182
Trading securities fair value, current $ 5,132,870