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Fair Value Measurements - Additional Information (Detail) - USD ($)
6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Jun. 30, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value measurements assets, significant transfers from level 1 to level 2 $ 0   $ 0
Fair value measurements assets, significant transfers from level 2 to level 1 0   0
Fair value measurements liabilities, significant transfers from level 1 to level 2 0   0
Fair value measurements liabilities, significant transfers from level 2 to level 1 0   $ 0
Senior notes   $ 791,700,000  
4.875% Senior Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Estimated fair value of senior loans $ 622,500,000 $ 645,700,000  
Interest rate of long-term debt 4.875% 4.875%  
Senior notes $ 592,400,000 $ 592,000,000  
5.25% Senior Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Estimated fair value of senior loans $ 447,000,000 $ 468,000,000  
Interest rate of long-term debt 5.25% 5.25%  
Senior notes $ 422,600,000 $ 422,400,000  
5.00% Senior Notes [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Estimated fair value of senior loans   $ 823,800,000  
Interest rate of long-term debt 5.00% 5.00%  
Senior notes   $ 791,700,000  
Redemption details In March 2018, we redeemed our 5.00% senior notes in full    
Senior term loans [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Estimated fair value of senior loans $ 742,500,000 199,900,000  
Senior term loans $ 743,700,000 $ 193,500,000