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Cash and Cash Equivalents and Short-term Investments (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2019
Sep. 30, 2019
Dec. 31, 2018
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2017
Investments:            
Trading securities, cost     $ 275,000      
Total short term, cost     275,000      
Trading securities           $ 238,000
Total short term     $ 330,000      
Financial institutions minimum net worth $ 1,000,000,000 $ 1,000,000,000        
Golden Tag            
Investments:            
Investment shares held (in shares)     7,500,000      
Ownership in property (as a percent)     10.00%      
Net proceeds from the sale of shares 113,000          
Loss on sale of shares   $ 217,000        
Trading securities            
Investments:            
Trading securities, cost     $ 275,000      
Interest and other income (expense), net | Golden Tag            
Investments:            
Loss on sale of shares $ 57,000          
Estimated Fair Value.            
Investments:            
Trading securities     330,000      
Total short term     330,000      
Estimated Fair Value. | Trading securities            
Investments:            
Trading securities     330,000      
Carrying Value.            
Investments:            
Trading securities     330,000      
Total short term     330,000      
Carrying Value. | Trading securities            
Investments:            
Trading securities     $ 330,000      
San Diego | Golden Tag            
Investments:            
Ownership in property (as a percent)       50.00% 50.00%