Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Narrative) (Details)

v3.21.1
Fair Value Measurements (Narrative) (Details)
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Assets, fair value $ 17,566,000  
Caelum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment owned, fair value 17,600,000 $ 11,100,000
Assets, fair value $ 17,566,000  
Caelum [Member] | Share Price [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input | $ / shares 2.43 1.54
Caelum [Member] | Risk Free Interest Rate [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input 0.0036 0.016
Caelum [Member] | Expected Volatility [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input 0.70 0.70
Caelum [Member] | Discount for Lack of Marketability [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input   0.287
Caelum [Member] | Discount for Lack of Marketability [Member] | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input 0.210  
Caelum [Member] | Discount for Lack of Marketability [Member] | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment, measurement input 0.310