Noncontrolling Interest - Common Shares and Units Activity (Details)	5 Months Ended
Jun. 13, 2025 shares
Equity Commonwealth
Increase (Decrease) in Stockholders' Equity
Noncontrolling ownership interest in the Operating Trust	0.14%
EQC Operating Trust
Increase (Decrease) in Stockholders' Equity
Noncontrolling ownership interest in the Operating Trust	0.05%
Common Shares, OP Units and LTIP Units
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	107,483,280
Repurchased and surrender of shares (in shares)	(510,000)
OP Unit Redemption (in shares)	0
Share-based compensation grants and vesting, net of forfeitures (in shares)	932,430
Ending balance (in shares)	107,905,710
Common Shares
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	107,335,177
Repurchased and surrender of shares (in shares)	(510,000)
OP Unit Redemption (in shares)	52,549
Share-based compensation grants and vesting, net of forfeitures (in shares)	873,406
Ending balance (in shares)	107,751,132
OP Units and LTIP Units(1)
Increase (Decrease) in Stockholders' Equity
Beginning balance (in shares)	148,103
Repurchased and surrender of shares (in shares)	0
OP Unit Redemption (in shares)	(52,549)
Share-based compensation grants and vesting, net of forfeitures (in shares)	59,024
Ending balance (in shares)	154,578
LTIP Units
Increase (Decrease) in Stockholders' Equity
Ending balance (in shares)	101,634

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares issued which are neither cancelled nor held in the treasury.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of shares issued during the period upon the conversion of units. An example of a convertible unit is an umbrella partnership real estate investment trust unit (UPREIT unit).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-SubTopic 10
-Topic 505
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480008/505-10-S99-1

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481112/505-10-50-3

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesConversionOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).

+ References

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares that have been repurchased and retired during the period.

+ References

+ Details

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_OwnershipAxis=eqc_EquityCommonwealthMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=eqc_EQCOperatingTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=eqc_CommonStockLongTermIncentivePlanUnitsAndOperatingPartnershipUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=eqc_LongTermIncentivePlanUnitsAndOperatingPartnershipUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=eqc_LongTermIncentivePlanUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: