Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Schedule of Financial Instruments, Measured at Fair Value on a Recurring Basis) (Details)

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Fair Value Measurements (Schedule of Financial Instruments, Measured at Fair Value on a Recurring Basis) (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Assets      
Assets, fair value $ 17,566    
Caelum [Member]      
Assets      
Assets, fair value 17,566    
Liabilities      
Liabilities, fair value     $ 11,148
Warrants [Member]      
Liabilities      
Liabilities, fair value   $ 27  
Convertible Notes [Member] | Caelum [Member]      
Liabilities      
Liabilities, fair value     11,148
Level 3 [Member]      
Assets      
Assets, fair value 17,566    
Level 3 [Member] | Caelum [Member]      
Assets      
Assets, fair value $ 17,566    
Liabilities      
Liabilities, fair value     11,148
Level 3 [Member] | Warrants [Member]      
Liabilities      
Liabilities, fair value   $ 27  
Level 3 [Member] | Convertible Notes [Member] | Caelum [Member]      
Liabilities      
Liabilities, fair value     $ 11,148