4. Property and Equipment, net  | 
6 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Jun. 30, 2018  | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property, Plant and Equipment [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Property and Equipment, net | 
 
 Property and equipment, net consists of the following: 
 
 
 Depreciation expense was approximately $5,000 and $6,000 for the three months ended June 30, 2018 and 2017, respectively, and approximately $11,000 and $14,000 for the six months ended June 30, 2018 and 2017, respectively.  | 
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