Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Contingent Consideration Liabilities (Detail)

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Commitments and Contingencies - Contingent Consideration Liabilities (Detail) - USD ($)
$ in Millions
Sep. 30, 2018
Dec. 31, 2017
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of contingent consideration liability $ 74.3 $ 65.7