Consulting fee.

No definition available.

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Namespace Prefix:	cgem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Consulting fee per month.

+ References

No definition available.

+ Details

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Namespace Prefix:	cgem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Management and advisory services.

+ References

No definition available.

+ Details

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Namespace Prefix:	cgem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Royalty percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	cgem_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

A description of the related party transaction, including transactions to which no amounts or nominal amounts were ascribed and such other information deemed necessary to an understanding of the effects of the transactions on the financial statements. Examples of common related party transactions are, sales, purchases and transfers of realty and personal property, services received or furnished, loans and leases to and from top management and affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919370-209981

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121603689&loc=d3e36975-112693

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918703-209980

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121606570&loc=SL77919784-209982

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(23))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of selling, general and administrative expenses resulting from transactions, excluding transactions that are eliminated in consolidated or combined financial statements, with related party.

+ References

No definition available.

+ Details

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

- Definition

Amount of expense related to royalty payments under a contractual arrangement such as payment for mineral and drilling rights and use of technology or intellectual property.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=cgem_GlobewaysHoldingsLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=cgem_TwoThousandTwentyConsultingAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=cgem_MPMOncologyCharitableFoundationIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=cgem_UBSOptimusFoundationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cgem_MPMCapitalMember
Namespace Prefix:
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Related Party Transactions - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Royalty percentage		1.00%
Royalties under obligation		$ 0		$ 0
Globeways Holdings Limited \| 2020 Consulting Agreement
Related Party Transaction [Line Items]
Related party transaction, description of transaction		In April 2020, the Company entered into a consulting agreement, or the 2020 Consulting Agreement, with Globeways Holdings Limited, or Globeways. Globeways and entities affiliated with F2 Ventures beneficially own in the aggregate greater than five percent of the Company’s outstanding units and Globeways is beneficially owned by a member of the Company’s board of directors.
Consulting fee per month	$ 25,000
MPM Oncology Charitable Foundation, Inc.
Related Party Transaction [Line Items]
Royalty percentage		0.50%
UBS Optimus Foundation
Related Party Transaction [Line Items]
Royalty percentage		0.50%
Maximum
Related Party Transaction [Line Items]
Management and advisory services		$ 0	$ 100,000
Maximum \| Globeways Holdings Limited \| 2020 Consulting Agreement
Related Party Transaction [Line Items]
Consulting fee		100,000
Maximum \| MPM Capital
Related Party Transaction [Line Items]
General and administrative expense		$ 100,000	$ 100,000