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Debt and Credit Agreements - Schedule of Debt (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Debt Instrument [Line Items]    
Unamortized debt issuance costs $ (2,491) $ (3,076)
Long-term debt 946,509 1,133,924
Current portion of long-term debt $ 0 188,000
6.51% weighted-average senior notes    
Debt Instrument [Line Items]    
Weighted average interest rate 6.51%  
Total debt $ 37,000 37,000
5.58% weighted-average senior notes    
Debt Instrument [Line Items]    
Weighted average interest rate 5.58%  
Total debt $ 87,000 175,000
Current portion of long-term debt   88,000
3.65% weighted-average senior notes    
Debt Instrument [Line Items]    
Weighted average interest rate 3.65%  
Total debt $ 825,000 925,000
Current portion of long-term debt $ 100,000 $ 100,000