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Fair Value of Financial Instruments (Other Investments - AVCT) (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]    
Equity investments, adjusted cost basis, amount $ 17.0 $ 18.0
AVCT [Member]    
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]    
Equity investment ownership percentage 9.00% 21.00%
Beneficial ownership of all interests percentage 21.00% 21.00%
Equity investment and warrants, amount paid (in dollars) $ 5.0  
Unrealized fair value measurement gains, net, AVCT shares 10.1  
Unrealized gains on AVCT convertible debentures, before tax 1.8  
Unrealized gains on AVCT convertible debentures, net of tax 1.4  
Equity investments, adjusted cost basis, amount   $ 2.0
AVCT [Member] | Common Stock [Member]    
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]    
Equity securities, fair value $ 17.0