The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

License Agreements - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2016	Apr. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
License Agreement [Line Items]
Research and development			$ 100,392,000	$ 89,398,000
City of Hope
License Agreement [Line Items]
Annual license fee		$ 25,000
Payment for execution of agreements			$ 75,000	50,000	$ 4,500,000
City of Hope \| Sponsored Research Agreement
License Agreement [Line Items]
Research and development				$ 100,000
City of Hope \| Maximum
License Agreement [Line Items]
Development and commercialization milestone payment		$ 3,200,000
California Institute Of Technology \| Maximum \| Co Exclusive License Agreement
License Agreement [Line Items]
Development and regulatory milestone payments	$ 7,200,000
California Institute Of Technology \| Minimum \| Co Exclusive License Agreement
License Agreement [Line Items]
Annual minimal royalty fee	$ 20,000