Fair Value Measurements - Schedule of Reconciliation of CVR Liability (Detail) - Level 3 Inputs [Member] - Contingent Value Right [Member] $ in Millions	3 Months Ended
	Mar. 31, 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	11.3	[1]
Fair value as of March 31, 2018	$ 18.2

[1] Unrealized gains and losses related to the revaluation of the CVR are recorded in other expense, net within the Company’s consolidated statements of income.