Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details) - Senior Notes [Member] - USD ($)
Dec. 31, 2017
Jun. 30, 2017
Dec. 31, 2016
Jun. 30, 2015
Mar. 31, 2013
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 $ 175,228,000   $ 177,625,000        
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 $ 326,250,000   $ 325,500,000        
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 $ 337,500,000   $ 324,750,000        
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 $ 214,000,000   $ 202,500,000        
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% senior notes [Member] | Level 2 [Member]              
Debt Instrument [Line Items]              
Aggregate Principal $ 300,000,000            
Fair value of fixed-rate debt              
Estimated Fair Value $ 305,250,000            
1.875% convertible senior notes [Member]              
Fair value of fixed-rate debt              
Debt instrument, stated rate 1.875%   1.875%        
1.875% convertible senior notes [Member] | Level 2 [Member]              
Debt Instrument [Line Items]              
Aggregate Principal     $ 126,500,000        
Fair value of fixed-rate debt              
Estimated Fair Value     $ 126,105,000