Additional per rentable square foot tenant improvement allowance to be contributed.

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Amortized over period.

+ References

No definition available.

+ Details

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Namespace Prefix:	cdr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Annual escalator percentage to be paid on each anniversary of rent commencement.

+ References

No definition available.

+ Details

Name:	cdr_AnnualEscalatorPercentageToBePaidOnEachAnniversaryOfRentCommencement
Namespace Prefix:	cdr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Annual net rent amount to be paid upon completion of building.

+ References

No definition available.

+ Details

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

- Definition

Free rent period.

+ References

No definition available.

+ Details

Name:	cdr_FreeRentPeriod
Namespace Prefix:	cdr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Initial annual net rent amount to be paid upon completion of building.

+ References

No definition available.

+ Details

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

- Definition

Landlord contribution to be made per rentable square foot toward cost of tenant improvements.

+ References

No definition available.

+ Details

Name:	cdr_LandlordContributionToBeMadePerRentableSquareFootTowardCostOfTenantImprovements
Namespace Prefix:	cdr_
Data Type:	srt-types:perUnitItemType
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Period Type:	duration

- Definition

Lease agreement entered date.

+ References

No definition available.

+ Details

Name:	cdr_LeaseAgreementEnteredDate
Namespace Prefix:	cdr_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of member workforce.

+ References

No definition available.

+ Details

Name:	cdr_NumberOfMemberWorkforce
Namespace Prefix:	cdr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Tenant credit.

+ References

No definition available.

+ Details

Name:	cdr_TenantCredit
Namespace Prefix:	cdr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The charge against earnings in the period to reduce the carrying amount of real property to fair value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230

+ Details

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

- Definition

Term of lessee's operating lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ 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=121609121&loc=SL77918673-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of lessor's operating lease that has not yet commenced.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919359-209981

+ Details

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

- Definition

Net cash outflow for the allowance granted to lessee and/or direct costs incurred by lessor used to prepare the leased premises for tenant's occupancy; for costs that are essential to originating the lease and would not otherwise have been incurred without the lease agreement, including but not limited to, evaluating the lessee's credit condition, guarantees, and collateral and costs incurred in negotiating, processing, and executing the lease agreement; and for any commission(s) incurred.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow from the acquisition of a piece of land, anything permanently fixed to it, including buildings, structures on it and so forth; includes real estate intended to generate income for the owner; excludes real estate acquired for use by the owner.

+ 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
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_RealEstatePropertiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_LeaseContractualTermAxis=cdr_CommercialLeaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstatePropertiesAxis=cdr_DevelopmentAssetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=cdr_GovernmentOfDistrictOfColumbiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAxis=cdr_Between10thAnd12thLeaseYearsMember
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:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=cdr_GirardPlazaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=cdr_MetroSquareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=cdr_WestBridgewaterPlazaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=cdr_RealEstateHeldForSaleMember
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Real Estate (Narrative) (Details)			12 Months Ended
Real Estate (Narrative) (Details)	Jul. 23, 2020 USD ($) Memberworkforce $ / ft²	Jun. 19, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Real Estate Properties [Line Items]
Purchase price				$ 9,083,000	$ 179,000
Impairment charges			$ 7,607,000	8,938,000	20,689,000
Commercial Lease Agreement [Member] \| Development Asset [Member] \| Government of the District of Columbia (“District”) [Member]
Real Estate Properties [Line Items]
Lease agreement entered date	Jul. 23, 2020
Number of member workforce planned to house new office headquarters \| Memberworkforce	700
Term of lease	20 years 10 months
Lessor, operating lease not yet commenced, Description			The Company anticipates commencement of construction to occur in the first quarter of 2021 and currently estimates that the space will be delivered during the end of the fourth quarter 2022
Initial annual net rent amount to be paid upon completion of building	$ 5,400,000
Annual escalator percentage to be paid on each anniversary of rent commencement	2.50%
Operating costs, property taxes and amortization of tenant improvements	$ 8,100,000
Annual net rent amount to be paid upon completion of building	$ 13,500,000
Free rent period	10 months
Tenant credit against either annual rent or any other tenant payment obligations including tenant improvement costs, in excess of tenant improvement allowance	$ 6,800,000
Amortized over period	240 months
Commercial Lease Agreement [Member] \| Development Asset [Member] \| Government of the District of Columbia (“District”) [Member] \| Between the 10th and 12th Lease Years [Member]
Real Estate Properties [Line Items]
Additional per rentable square foot tenant improvement allowance to be contributed \| $ / ft²	9.38
Commercial Lease Agreement [Member] \| Development Asset [Member] \| Government of the District of Columbia (“District”) [Member] \| Maximum [Member]
Real Estate Properties [Line Items]
Landlord contribution to be made per rentable square foot toward cost of tenant improvements \| $ / ft²	155
Girard Plaza [Member]
Real Estate Properties [Line Items]
Purchase price		$ 8,500,000
Metro Square [Member]
Real Estate Properties [Line Items]
Impairment charges			$ 7,200,000
West Bridgewater Plaza [Member]
Real Estate Properties [Line Items]
Impairment charges					9,400,000
Real Estate Held for Sale [Member]
Real Estate Properties [Line Items]
Impairment charges			$ 400,000	$ 8,900,000	$ 11,300,000