Fair Value Measurements - Additional Information (Details)		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 27, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jul. 01, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jul. 01, 2017 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers among level 1, 2, and 3		$ 0		$ 0				$ 0
Cash proceeds from divestiture of businesses				1,300,000	$ 37,200,000
Change in financial assets		600,000	$ (38,700,000)	(9,000,000)	(21,600,000)
Net gain on reduction of contingent consideration					15,600,000
Measured on a recurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Potential contingent milestone payments		125,500,000		125,500,000				134,500,000
Royalty Pharma Contingent Milestone Payments | Measured on a recurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Potential contingent milestone payments										$ 184,500,000
Increase (decrease) in fair value of milestone payment		600,000	(39,200,000)	(9,000,000)	(39,200,000)
Estimated fair valued contingent milestone payment		125,500,000	145,800,000	$ 125,500,000	$ 145,800,000			$ 134,500,000	$ 124,900,000	$ 184,500,000	$ 0
Royalty Pharma 2018 Contingent Milestone Payments | Measured on a recurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase (decrease) in fair value of milestone payment		(2,900,000)
Royalty Pharma 2020 Contingent Milestone Payments | Measured on a recurring basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase (decrease) in fair value of milestone payment		$ 3,500,000
Scenario, Forecast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Potential contingent milestone payments						$ 60,200,000	$ 65,300,000
Fair value adjustment						400,000,000	250,000,000
Change in financial assets						339,800,000	184,700,000
Net sales threshold for milestone payment						$ 1,950,000,000	$ 1,850,000,000
Specialty Sciences
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain related to Royalty Pharma			$ 17,100,000
Royalty Pharma
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sale price of divestiture - cash plus non-cash	$ 2,850,000,000
Cash proceeds from divestiture of businesses	2,200,000,000
2018 milestone payment	250,000,000
2020 milestone payment	$ 400,000,000
Rate of return				8.09%	8.05%
Measurement Input, Price Volatility | Royalty Pharma
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility rate assumed		0.300	0.300	0.300	0.300