Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Reconciliation of CVR Liability (Detail)

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Fair Value Measurements - Schedule of Reconciliation of CVR Liability (Detail) - Level 3 Inputs [Member] - Contingent Value Right [Member]
$ in Millions
9 Months Ended
Sep. 30, 2018
USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]  
Fair value as of December 31, 2017 $ 6.9
Net unrealized loss 11.4 [1]
Fair value as of September 30, 2018 $ 18.3
[1] Unrealized gains and losses related to the revaluation of the CVR are recorded in Other expense, net within the Company’s condensed consolidated statements of income.