Annual report pursuant to Section 13 and 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 ($)
Dec. 31, 2018
Dec. 31, 2017
Jun. 30, 2017
Jun. 30, 2015
Apr. 30, 2012
Dec. 31, 2010
4.50% senior notes [Member]            
Fair value of fixed-rate debt            
Debt instrument, stated rate 4.50% 4.50%        
4.50% senior notes [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 [Member]            
Debt Instrument [Line Items]            
Aggregate Principal           $ 200,000,000
Fair value of fixed-rate debt            
Debt instrument, stated rate 7.15% 7.15%       7.15%
7.15% senior notes [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 $ 307,500,000 $ 326,250,000        
7.00% senior notes [Member]            
Debt Instrument [Line Items]            
Aggregate Principal         $ 300,000,000  
Fair value of fixed-rate debt            
Debt instrument, stated rate 7.00% 7.00%     7.00%  
7.00% senior notes [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 309,750,000 $ 337,500,000        
6.00% senior notes [Member]            
Debt Instrument [Line Items]            
Aggregate Principal $ 400,000,000.0     $ 200,000,000.0    
Fair value of fixed-rate debt            
Debt instrument, stated rate 6.00% 6.00%   6.00%    
6.00% senior notes [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 $ 379,520,000 $ 214,000,000        
5.125% senior notes [Member]            
Debt Instrument [Line Items]            
Aggregate Principal     $ 300,000,000.0      
Fair value of fixed-rate debt            
Debt instrument, stated rate 5.125% 5.125% 5.125%      
5.125% senior notes [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 $ 255,750,000 $ 305,250,000