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Fair Value Measurements - Textuals (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2019
Dec. 31, 2018
Fair Value, Nonrecurring [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Gains or losses related to non-financial assets and liabilities $ 0 $ 0    
Senior Notes [Member] | 5.125% Senior Notes Due 2023 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt instrument interest rate (percent)     5.125% 5.125%
Senior Notes [Member] | 5.75% Senior Notes Due 2024 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt instrument interest rate (percent)     5.75% 5.75%
Senior Notes [Member] | 5.75% Senior Notes Due 2025 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt instrument interest rate (percent)     5.75% 5.75%
Senior Notes [Member] | 4.50% Senior Notes due 2028 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt instrument interest rate (percent)     4.50%  
Senior Notes [Member] | 4.75% Senior Notes due 2030 [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt instrument interest rate (percent)     4.75%