Annual report pursuant to Section 13 and 15(d)

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

v3.20.4
FAIR VALUE DISCLOSURES - Schedule of Fair Value of Fixed-Rate Debt (Details) - Senior Notes [Member] - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Mar. 31, 2018
Jun. 30, 2017
Jun. 30, 2015
Apr. 30, 2012
Dec. 31, 2011
4.50% senior notes [Member]              
Fair value of fixed-rate debt              
Debt instrument, stated rate     4.50%        
7.15% senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal             $ 200,000,000.0
Fair value of fixed-rate debt              
Debt instrument, stated rate             7.15%
7.00% senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal           $ 300,000,000.0  
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 319,758,000 $ 327,390,000          
6.00% senior notes [Member]              
Debt Instrument [Line Items]              
Aggregate Principal $ 200,000,000.0       $ 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 $ 400,000,000          
Fair value of fixed-rate debt              
Estimated  Fair Value $ 451,913,000 $ 449,200,000          
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 $ 333,328,000 $ 319,500,000