Annual report pursuant to Section 13 and 15(d)

SENIOR NOTES, NET - Schedule of Senior and Convertible Senior Notes (Descriptors) (Details)

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SENIOR NOTES, NET - Schedule of Senior and Convertible Senior Notes (Descriptors) (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 due 2018 [Member]            
Debt Instrument [Line Items]            
Senior and convertible senior notes, gross $ 0 $ 175,000,000        
Debt instrument, stated rate 4.50% 4.50%        
7.15% senior notes due 2020 [Member]            
Debt Instrument [Line Items]            
Senior and convertible senior notes, gross $ 300,711,000 $ 301,280,000        
Aggregate Principal           $ 200,000,000
Debt instrument, stated rate 7.15% 7.15%       7.15%
Unamortized premium $ 711,000 $ 1,280,000        
7.00% senior notes due 2022 [Member]            
Debt Instrument [Line Items]            
Senior and convertible senior notes, gross $ 300,000,000 $ 300,000,000        
Aggregate Principal         $ 300,000,000  
Debt instrument, stated rate 7.00% 7.00%     7.00%  
6.00% senior notes due 2025 [Member]            
Debt Instrument [Line Items]            
Senior and convertible senior notes, gross [1] $ 405,318,000 $ 200,000,000        
Aggregate Principal $ 400,000,000.0     $ 200,000,000.0    
Debt instrument, stated rate 6.00% 6.00%   6.00%    
Unamortized premium   $ 0        
5.125% senior notes due 2027 [Member]            
Debt Instrument [Line Items]            
Senior and convertible senior notes, gross $ 300,000,000 $ 300,000,000        
Aggregate Principal     $ 300,000,000.0      
Debt instrument, stated rate 5.125% 5.125% 5.125%      
[1] (1) $200.0 million of the total $400.0 million of 6.00% Senior Notes due 2025 outstanding at December 31, 2018 was issued at par and had no unamortized premium.