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Financial Instruments (Narrative) (Details)
$ in Millions
1 Months Ended
Aug. 31, 2017
USD ($)
a
Jun. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Number of acres | a 6    
Proceeds from sale of property, plant, and equipment $ 12.2    
Promissory note received in sale of property, plant, and equipment $ 5.7    
Stated interest rate on promissory note 3.50%    
Unsecured debt [Member] | Level 2 [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Unsecured notes   $ 375.0 $ 375.0