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Fair Value Measurements - Carrying Value and Fair Value of Debt (Detail) - USD ($)
$ in Millions
Jun. 30, 2018
Dec. 31, 2017
Carrying Value | Term Loan Facility [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value $ 350.0  
Carrying Value | Senior Unsecured Notes [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value 893.3 $ 892.6
Carrying Value | Revolving Credit Facility [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value 900.0 615.0
Fair Value | Term Loan Facility [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value 350.0  
Fair Value | Senior Unsecured Notes [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value 898.5 926.3
Fair Value | Revolving Credit Facility [Member]    
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]    
Fair Value $ 900.0 $ 615.0