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Summary of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Dec. 31, 2022
USD ($)
segment
country
$ / shares
Dec. 31, 2021
USD ($)
$ / shares
Dec. 31, 2022
GBP (£)
country
Accounting Policies [Line Items]      
Changes in lease liability $ 40,000 $ 172,000  
Cash exceeding balance insured by FDIC 17,800,000    
Cash balance insured by FSCS | £     £ 85,000
Cash exceeding balance insured by FSCS $ 200,000    
Number of operating segments | segment 1    
Number of reportable segments | segment 1    
Number of geographic areas for development operations | country 2   2
Cash and cash equivalents $ 18,345,000 36,559,000  
Tax on other comprehensive income (loss) 0 0  
Reclassifications out of other comprehensive income (loss) $ 0 $ 0  
Common stock, par value (in dollars per share) | $ / shares $ 0.001 $ 0.001  
Right-of-use lease asset $ 142,000 $ 30,000  
Board Director [Member]      
Accounting Policies [Line Items]      
Stock awards vesting period 1 year    
Minimum      
Accounting Policies [Line Items]      
Stock awards vesting period 3 years    
Maximum      
Accounting Policies [Line Items]      
Cash balances insured by FDIC $ 250,000    
Stock awards vesting period 4 years    
Property, plant and equipment | Minimum      
Accounting Policies [Line Items]      
Estimated useful life 3 years    
Property, plant and equipment | Maximum      
Accounting Policies [Line Items]      
Estimated useful life 5 years    
Leasehold improvements | Minimum      
Accounting Policies [Line Items]      
Estimated useful life 2 years    
Leasehold improvements | Maximum      
Accounting Policies [Line Items]      
Estimated useful life 15 years