Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details) - Senior Notes [Member] - USD ($)
Dec. 31, 2016
Dec. 31, 2015
Jun. 02, 2015
Mar. 31, 2013
Sep. 30, 2012
Apr. 30, 2012
Dec. 31, 2010
4.50% senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal       $ 175,000,000      
Fair value of fixed-rate debt              
Debt instrument, stated rate 4.50% 4.50%   4.50%      
4.50% senior notes [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 $ 177,625,000 $ 175,000,000          
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 $ 325,500,000 $ 315,750,000          
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 $ 324,750,000 $ 313,500,000          
6.00% senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal     $ 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 $ 200,000,000 $ 200,000,000          
Fair value of fixed-rate debt              
Estimated Fair Value $ 202,500,000 $ 197,500,000          
1.875% convertible senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal         $ 126,500,000    
Fair value of fixed-rate debt              
Debt instrument, stated rate 1.875% 1.875%     1.875%    
1.875% convertible senior notes [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 $ 126,105,000 $ 124,128,000