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Long-Term Debt - Narrative (Details) - 2017/2018 Senior Notes due December 2025 - USD ($)
1 Months Ended
Mar. 31, 2018
May 31, 2018
2013 Senior Notes due in March 2018 and March 2023    
Debt Instrument [Line Items]    
Repayments of debt $ 250,000,000.0  
2018 Senior Notes due December 2025    
Debt Instrument [Line Items]    
Principal amount of debt instrument   $ 500,000,000.0
Stated interest rate (as a percent)   6.75%