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Indebtedness - Senior Subordinated Notes Exchange- Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Sep. 30, 2016
Dec. 31, 2017
Oct. 05, 2017
Dec. 31, 2016
Sep. 16, 2016
5.00% Senior Notes Due 2023          
Debt Instrument [Line Items]          
Interest rate on notes 5.00% 5.00% 5.00% 5.00% 5.00%
Maturity date of loan   Mar. 15, 2023      
5.00% Senior Notes Due 2022          
Debt Instrument [Line Items]          
Interest rate on notes 5.00% 5.00% 5.00% 5.00% 5.00%
Maturity date of loan   Aug. 15, 2022      
5.75% Senior Notes Due 2021          
Debt Instrument [Line Items]          
Interest rate on notes 5.75% 5.75% 5.75% 5.75% 5.75%
Maturity date of loan   Jun. 01, 2021      
Senior Notes          
Debt Instrument [Line Items]          
Additional interest expense on senior subordinated notes exchange $ 6.6        
Premium recorded in connection with debt exchange   $ 3.5      
Percentage of premium received on face amount tendered in exchange of debt   95.00%      
Maximum redemption price of notes as percentage of principal amount   101.00%