Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands		6 Months Ended
Mar. 04, 2020	Jun. 30, 2022
Loss Contingencies [Line Items]
Loss contingency, answer, affirmative defenses and counterclaims filing date	May 26, 2020
Loss contingency, answer and counterclaims by plaintiff filing date	Jun. 05, 2020
Patent Infringement Lawsuit
Loss Contingencies [Line Items]
Lawsuit filed date	March 4, 2020
Name of plaintiff		Vytacera Bio, LLC
Loss contingency claim amount		$ 0

Loss contingency answer, affirmative defenses and counterclaims filing date.

No definition available.

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Namespace Prefix:	ctmx_
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- Definition

Loss contingency, answer and counterclaims by plaintiff filing date.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124440162&loc=d3e12021-110248

+ Details

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

- Definition

States the date the complaint was formally filed in a court of law, in arbitration or mediation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

+ Details

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- Definition

Identifies the plaintiff in the lawsuit.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
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+ Details

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- Details

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