Summary of Significant Accounting Policies - Segment Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2025 USD ($) segment	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Segment Information
Number of operating segments \| segment	1
Number of reportable segments \| segment	1
Research and development	$ 245,074	$ 163,550	$ 118,011
Single reportable segment
Segment Information
Research and development	245,074	163,550	118,011
Single reportable segment \| Barzolvolimab/Anti-KIT Program
Segment Information
Research and development	198,329	123,750	79,913
Single reportable segment \| CDX-622
Segment Information
Research and development	18,958	17,341	16,299
Single reportable segment \| Other Programs
Segment Information
Research and development	$ 27,787	$ 22,459	$ 21,799

Amount of expense for research and development. Includes, but is not limited to, cost for computer software product to be sold, leased, or otherwise marketed and writeoff of research and development assets acquired in transaction other than business combination or joint venture formation or both. Excludes write-down of intangible asset acquired in business combination or from joint venture formation or both, used in research and development activity.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 18
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
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-Name Accounting Standards Codification
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-Publisher FASB
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 730
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Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 912
-SubTopic 730
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479532/912-730-25-1

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration