Commitments and Contingencies (Details) - USD ($) $ in Millions		1 Months Ended						3 Months Ended
	Jul. 02, 2020	Sep. 30, 2019	Apr. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Nov. 30, 2018	Oct. 31, 2018	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Apr. 28, 2021
Other Commitments [Line Items]
Research and development								$ 289.1	$ 200.9
Collaboration Agreement, Milestone Payments To Be Made Next Twelve Months								155.1
Gain (Loss) on Disposition of Assets								25.3	$ 0.0
Canadian Patented Medicine Prices Review Board
Other Commitments [Line Items]
Loss Contingency, Estimate of Possible Loss								54.7
Canadian Patented Medicine Prices Review Board | Subsequent Event
Other Commitments [Line Items]
Escrow Deposit																$ 80.9
SEC
Other Commitments [Line Items]
Litigation Settlement, Amount Awarded to Other Party	$ 21.5
DOJ And OIG
Other Commitments [Line Items]
Loss Contingency Accrual, Payments			$ 13.1
Syntimmune, Inc
Other Commitments [Line Items]
Asset Acquisition, Contingent Consideration, Milestone Payments						$ 800.0
Astellas Pharam [Member]
Other Commitments [Line Items]
Asset Acquisition, Contingent Consideration, Milestone Payments								71.5
Zealand
Other Commitments [Line Items]
Payments to Acquire Equity Method Investments				$ 13.8
Eidos
Other Commitments [Line Items]
Payments to Acquire Equity Method Investments		$ 19.9
Dicerna
Other Commitments [Line Items]
Payments to Acquire Equity Method Investments							$ 10.3
Subcutaneous Formulation | Syntimmune, Inc
Other Commitments [Line Items]
Asset Acquisition, Contingent Consideration, Milestone Payments						$ 130.0
Collaboration and License Agreement
Other Commitments [Line Items]
Potential future payments, milestone achievement								114.1
Zealand | Zealand
Other Commitments [Line Items]
Payments To Acquire Licenses And Equity Investment				40.0
Prepaid Research And Development Expense				$ 5.0								$ 5.0
Research and development												$ 21.2
Potential future payments, milestone achievement								610.0
Collaboration Agreement, Potential Future Payments, Additional Milestone Achievement								115.0
Collaboration Agreement, Potential Future Payments, Option Fee								15.0
Eidos | Affibody AB
Other Commitments [Line Items]
Payments To Acquire Licenses And Equity Investment		$ 50.0
Research and development											$ 30.1
Potential future payments, milestone achievement								30.0
Dicerna | Dicerna Pharmaceutical Collaboration Agreement
Other Commitments [Line Items]
Payments To Acquire Licenses And Equity Investment							$ 37.0
Research and development										$ 20.0			$ 26.7
Research and Development Arrangement, Potential Payment, Maximum								604.1
Halozyme Therapeutics, Inc | License Agreement 1
Other Commitments [Line Items]
Research and Development Arrangement, Potential Payment, Maximum								155.0
Research and development															$ 40.0
Research and Development Agreement, Option Fee								8.0
Research and Development Arrangement, Potential Contingent Payment, Maximum								160.0
Caelum | Collaborative Arrangement
Other Commitments [Line Items]
Potential future payments, milestone achievement					$ 30.0
Milestone payments to be made in next 12 months								14.0
Maximum potential future payment								500.0
Upfront option exercise payment								150.0
Maximum regulatory and commercial milestone payments								350.0
Origin Biosciences
Other Commitments [Line Items]
Gain (Loss) on Disposition of Assets								20.0						$ 3.5
Asset Sale, Contingent Payments To Be Received								21.0
Other Third Party Manufacturers
Other Commitments [Line Items]
Remaining total commitments								125.7
Lonza Group AG
Other Commitments [Line Items]
Remaining total commitments								1,432.1
Unrecorded Unconditional Purchase Obligation, Undiscounted Fixed Payment Amount								$ 97.9