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Fair Value Measurements (Additional Disclosures Regarding Fair Value Measurements) (Details) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Nov. 15, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Senior Notes, Carrying Value $ 742,926,000 $ 741,825,000  
Level 2 | Fair Value      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Closing trading price per $100 as of the last day of trading for the year 100    
Senior Notes      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Senior Notes, Carrying Value 742,926,000    
Senior Notes | Level 2 | Fair Value      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Senior Notes, Fair Value 813,998,000    
Unsecured Debt | Unsecured Senior Notes due December 2027      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Principal amount of notes $ 750,000,000.0   $ 750,000,000.0