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Fair Value Measurements (Narrative) (Details) - USD ($)
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Held-to-maturity impairment $ 0 $ 0  
Long-term debt, fair value 37,296,000   $ 38,402,000
Long-term debt, book value 37,021,000   37,967,000
Held-to-maturity Securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Allowance for credit loss $ 0   $ 0