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Debt - Schedule of the Company's Debt (Parenthetical) (Detail)
12 Months Ended
Aug. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Jun. 30, 2017
Jun. 07, 2017
11.25% Senior Notes Due February 1, 2019          
Debt Instrument [Line Items]          
Interest rate   11.25%      
Maturity date     Feb. 01, 2019    
Effective interest rate     13.25%    
7.625% Senior Notes Due June 15, 2020          
Debt Instrument [Line Items]          
Interest rate   7.625%      
Maturity date   Jun. 15, 2020      
7.875% Senior Notes Due March 15, 2021          
Debt Instrument [Line Items]          
Interest rate   7.875%      
Maturity date   Mar. 15, 2021      
8.875% Debentures Due April 15, 2021          
Debt Instrument [Line Items]          
Interest rate   8.875%      
Maturity date   Apr. 15, 2021      
7.00% Senior Notes Due February 15, 2022          
Debt Instrument [Line Items]          
Interest rate 7.00% 7.00%      
Maturity date Feb. 15, 2022 Feb. 15, 2022      
6.50% Senior Notes Due November 15, 2023          
Debt Instrument [Line Items]          
Interest rate   6.50%      
Maturity date   Nov. 15, 2023      
6.00% Senior Notes Due April 1, 2024          
Debt Instrument [Line Items]          
Interest rate   6.00%   6.00%  
Maturity date   Apr. 01, 2024      
6.625% Debentures Due April 15, 2029          
Debt Instrument [Line Items]          
Interest rate   6.625%     6.625%
Maturity date   Apr. 15, 2029      
8.820% Debentures Due April 15, 2031          
Debt Instrument [Line Items]          
Interest rate   8.82%      
Maturity date   Apr. 15, 2031