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Fair Value Measurements - Fair Value of Debt (Details) - Fixed Rate Debt - Level 2 - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Fair Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Long-term debt, fair value $ 1,352,000 $ 1,371,000
Carrying Amount    
Fair Value, Balance Sheet Grouping, Financial Statement Captions    
Long-term debt, fair value $ 1,296,135 $ 1,295,867