Commitments and Contingencies - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Commitments And Contingencies [Line Items]
Contingent payments upon achievement of certain development and regulatory activities and commercial sales and licensing milestones	$ 494.4
Contingent consideration	144.4
Clinical and Post Marketing Services
Commitments And Contingencies [Line Items]
Purchase commitments and other minimum contractual obligations	84.0
Merck Serono
Commitments And Contingencies [Line Items]
Contingent payments upon achievement of certain development and regulatory activities and commercial sales and licensing milestones	156.7
Completed Programs | Merck Serono
Commitments And Contingencies [Line Items]
Contingent payments upon achievement of certain development and regulatory activities and commercial sales and licensing milestones	$ 80.6