Name:	epzm_OperatingLeaseRentExpenseIncrementalPercentage
Namespace Prefix:	epzm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

+ References

No definition available.

+ Details

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of lessee's operating lease that has not yet commenced. Including, but not limited to, nature of involvement with construction or design of underlying asset for lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980

+ Details

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

- Definition

Description of terms and conditions of option to extend lessee's operating lease that has not yet commenced. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability.

+ References

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

Name:	us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Net cash outflow or inflow from monetary allowance granted by the landlord to a tenant to entice tenant to move into landlords building which will enable the tenant to prepare the leased premises for tenants occupancy.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585

+ Details

Name:	us-gaap_PaymentsForProceedsFromTenantAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of an asset, typically cash, provided to a counterparty to provide certain assurance of performance by the entity pursuant to the terms of a written or oral agreement, such as a lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_SecurityDeposit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_StatementGeographicalAxis=epzm_HampshireStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=epzm_BMRHampshireLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=epzm_CambridgeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Leases - Additional Information (Detail) - USD ($)			6 Months Ended
Leases - Additional Information (Detail) - USD ($)	Aug. 11, 2021	Aug. 16, 2019	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Lessee Lease Description [Line Items]
Monthly base rent	$ 377,000,000		$ 200,000
Increase in base rent	388,000		33,000
Annual increase of base rent			9,000
Security deposit			500,000
Tenant Allowance	430,000
Operating Lease, Right-of-Use Asset	$ 7,000,000.0		18,124,000	$ 20,054,000
Hampshire Street [Member] \| Letter of Credit [Member]
Lessee Lease Description [Line Items]
Security deposit			$ 1,000,000.0		$ 1,000,000.0
Operating lease extend description	the Company extended the term of the Technology Square Lease through November 30, 2024
BMR-Hampshire LLC [Member] \| Cambridge [Member]
Lessee Lease Description [Line Items]
Operating lease description		the Company entered into a lease (the "Hampshire Street Lease") with BMR-Hampshire LLC ("BMR"). The Hampshire Street Lease is for 33,525 rentable square feet of office space in Cambridge, Massachusetts. The Hampshire Street Lease commenced as of December 1, 2019
Operating lease extend description		the Company with an option to extend the lease term for one additional five-year period
Operating lease rent expense		$ 200,000
Operating lease rent expense incremental percentage		2.50%