Annual report pursuant to Section 13 and 15(d)

Organization and summary of significant accounting policies (Management's plans and basis of presentation) (Details)

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Organization and summary of significant accounting policies (Management's plans and basis of presentation) (Details) - USD ($)
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]      
Cash and liquid investments $ 13,037,000    
Working capital 12,688,000    
Stockholders' equity 14,920,359 $ 16,070,636 $ 23,685,123
Accumulated deficit 109,855,276 $ 105,582,439  
Total value of capitalized patent costs considered 100% impaired $ 508,000