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Significant Accounting Policies (Details) - USD ($)
$ in Thousands
1 Months Ended 9 Months Ended
Apr. 30, 2019
Sep. 30, 2019
Jan. 01, 2019
Dec. 31, 2018
Significant Accounting Policies        
Minimum period for maturity dates for short-term investments   90 days    
Accumulated deficit   $ (443,878)   $ (435,684)
Lease accounting        
Operating lease liabilities   113    
Right of use operating assets   113    
Operating Lease, Liability, Current   $ 97    
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]   Accrued Liabilities, Current    
Operating Lease, Liability, Noncurrent   $ 16    
Minimum        
Lease accounting        
Lessee, Operating Lease, Renewal Term   6 months    
Maximum        
Lease accounting        
Lessee, Operating Lease, Renewal Term   2 years 6 months    
Guadalupe De Los Reyes, Mexico | Option Agreement Two        
Significant Accounting Policies        
Value of carrying value for option payment proceeds to be recognized as contract liability $ 0      
Accounting Standards Update 2016-02 | Restatement adjustment        
Lease accounting        
Operating lease liabilities     $ 186  
Right of use operating assets     $ 186