Quarterly report pursuant to Section 13 or 15(d)

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

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FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details) - Senior Notes [Member] - USD ($)
Mar. 31, 2017
Dec. 31, 2016
4.50% senior notes due 2018 [Member]    
Fair value of fixed-rate debt    
Debt instrument, stated rate (percent) 4.50% 4.50%
4.50% senior notes due 2018 [Member] | Level 2 [Member]    
Debt Instrument [Line Items]    
Aggregate Principal $ 175,000,000 $ 175,000,000
Fair value of fixed-rate debt    
Estimated Fair Value $ 178,063,000 $ 177,625,000
7.15% senior notes due 2020 [Member]    
Fair value of fixed-rate debt    
Debt instrument, stated rate (percent) 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 $ 328,080,000 $ 325,500,000
7.00% senior notes due 2022 [Member]    
Fair value of fixed-rate debt    
Debt instrument, stated rate (percent) 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 $ 336,000,000 $ 324,750,000
6.00% senior notes due 2025 [Member]    
Fair value of fixed-rate debt    
Debt instrument, stated rate (percent) 6.00% 6.00%
6.00% senior notes due 2025 [Member] | Level 2 [Member]    
Debt Instrument [Line Items]    
Aggregate Principal $ 200,000,000 $ 200,000,000
Fair value of fixed-rate debt    
Estimated Fair Value $ 208,380,000 $ 202,500,000
1.875% convertible senior notes due 2032 [Member]    
Fair value of fixed-rate debt    
Debt instrument, stated rate (percent) 1.875% 1.875%
1.875% convertible senior notes due 2032 [Member] | Level 2 [Member]    
Debt Instrument [Line Items]    
Aggregate Principal $ 126,500,000 $ 126,500,000
Fair value of fixed-rate debt    
Estimated Fair Value $ 126,026,000 $ 126,105,000