Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details)

v3.10.0.1
FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details) - Senior Notes [Member] - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Jun. 30, 2015
4.50% senior notes due 2018 [Member]      
Fair value of fixed-rate debt      
Stated interest rate 4.50% 4.50%  
4.50% senior notes due 2018 [Member] | Level 2 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal   $ 175,000,000  
Fair value of fixed-rate debt      
Estimated Fair Value   $ 175,228,000  
7.15% senior notes due 2020 [Member]      
Fair value of fixed-rate debt      
Stated interest rate 7.15% 7.15%  
7.15% senior notes due 2020 [Member] | Level 2 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal $ 300,000,000 $ 300,000,000  
Fair value of fixed-rate debt      
Estimated Fair Value $ 314,250,000 $ 326,250,000  
7.00% senior notes due 2022 [Member]      
Fair value of fixed-rate debt      
Stated interest rate 7.00% 7.00%  
7.00% senior notes due 2022 [Member] | Level 2 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal $ 300,000,000 $ 300,000,000  
Fair value of fixed-rate debt      
Estimated Fair Value 322,500,000 $ 337,500,000  
6.00% senior notes due 2025 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal $ 400,000,000.0    
Fair value of fixed-rate debt      
Stated interest rate 6.00% 6.00% 6.00%
6.00% senior notes due 2025 [Member] | Level 2 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal $ 400,000,000 $ 200,000,000  
Fair value of fixed-rate debt      
Estimated Fair Value $ 404,000,000 $ 214,000,000  
5.125% senior notes due 2027 [Member]      
Fair value of fixed-rate debt      
Stated interest rate 5.125% 5.125%  
5.125% senior notes due 2027 [Member] | Level 2 [Member]      
Debt Instrument [Line Items]      
Aggregate Principal $ 300,000,000 $ 300,000,000  
Fair value of fixed-rate debt      
Estimated Fair Value $ 276,390,000 $ 305,250,000