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Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands, € in Millions					1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 10, 2020 USD ($)	Dec. 10, 2020 EUR (€)	Oct. 23, 2020 USD ($)	Apr. 07, 2020 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 10, 2020 EUR (€)
Business Acquisition [Line Items]
Acquired in-process research and development expenses								$ 5,856,000	$ 4,251,000	$ 0
Stock-based compensation expense								$ 643,000	$ 636,000	$ 845,000
Discount rate of acquired IPR&D						8.00%		8.00%	9.50%
Foreign currency exchange rate						1.2		1.2
Three year senior unsecured term loan facility | Medium-term notes
Business Acquisition [Line Items]
Borrowing under the senior unsecured term loan facility					$ 1,000,000
Immunomedics, Inc.
Business Acquisition [Line Items]
Revenue since acquisition date								$ 49,000
Consideration			$ 20,600,000
Accelerated stock-based expense								289,000
Acquisition-related expenses						$ 615,000		39,000
Fair value step-up adjustment of inventories acquired			881,000
Inventories			946,000
Liability related to future royalties			1,100,000
Goodwill			$ 3,991,000
Immunomedics, Inc. | Measurement Input, Risk Free Interest Rate
Business Acquisition [Line Items]
Liability related to future royalties, measurement Input			0.025
Immunomedics, Inc. | Measurement Input, Expected Term
Business Acquisition [Line Items]
Liability related to future royalties, measurement Input			16
Immunomedics, Inc. | Payments to outstanding common stockholders
Business Acquisition [Line Items]
Cash payments made for acquisition			$ 20,400,000
Immunomedics, Inc. | Payments to equity award holders
Business Acquisition [Line Items]
Cash payments made for acquisition			242,000
Immunomedics, Inc. | Acquired IPR&D
Business Acquisition [Line Items]
Acquired IPR&D			$ 15,760,000
Discount rate of acquired IPR&D			7.00%
Immunomedics, Inc. | Intangible asset - Trodelvy for mTNBC
Business Acquisition [Line Items]
Finite-lived intangible asset			$ 4,600,000
Discount rate of finite-lived intangible asset acquired			7.00%
Estimated useful life of finite-lived intangible asset acquired			12 years
Immunomedics, Inc. | Outlicense contract
Business Acquisition [Line Items]
Finite-lived intangible asset			$ 175,000
Discount rate of finite-lived intangible asset acquired			7.00%
Estimated useful life of finite-lived intangible asset acquired			15 years
MYR
Business Acquisition [Line Items]
Consideration	$ 1,400,000	€ 1,200
Maximum potential future milestone payments	$ 360,000										€ 300
Forty Seven, Inc.
Business Acquisition [Line Items]
Share price | $ / shares				$ 95.50
Total consideration, net of acquired cash				$ 4,700,000
Acquired in-process research and development expenses				4,500,000			$ 4,500,000
Assets acquired				$ 202,000
Accelerated stock-based expense								$ 144,000

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