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Fair Value of Financial Instruments (Other Investments - AVCT) (Narrative) (Details) - AVCT [Member] - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]    
Equity investment ownership, percentage 9.00% 9.00%
Beneficial ownership of all interests, percentage 22.00% 21.00%
Equity investment and warrants, amount paid (in dollars) $ 5.0  
Unrealized fair value measurement gains (losses), AVCT shares (1.0)  
Unrealized gains (losses) on AVCT convertible debentures, before tax 1.0  
Unrealized gains (losses) on AVCT convertible debentures, net of tax 0.8  
Common Stock [Member]    
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]    
Equity securities, fair value $ 17.0 $ 17.0