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Fair Value Measurement (Details) - USD ($)
Sep. 30, 2019
Dec. 31, 2018
Short-term investments:    
Transfer of assets from Level 1 to 2 $ 0 $ 0
Transfer of assets from Level 2 to 1 0 0
Transfer of liabilities from Level 1 to 2 0 0
Transfer of liabilities from Level 2 to 1 0 0
Recurring    
Cash equivalent:    
Money market funds 15,050,000 50,000
Short-term investments:    
Term deposits 175,000 175,000
Total Assets 15,225,000 225,000
Level 1 | Recurring    
Cash equivalent:    
Money market funds 15,050,000 50,000
Short-term investments:    
Term deposits 175,000 175,000
Total Assets $ 15,225,000 $ 225,000