ORGANIZATION (Details)	6 Months Ended
Jun. 30, 2011
ORGANIZATION
Number of operating storage facilities in which the entity has equity interests	680
Number of properties owned by franchisees and third parties	180
Number of operating properties owned and/or managed	860
Number of states in which operating storage facilities are located	34
Number of reportable segments	3
Number of development projects in process	1
Maximum percentage of rental income accounted for by any single tenant (as a percent)	5.00%

Represents the maximum percentage of rental income accounted for by any single tenant.

Name:	exr_MaximumPercentageOfRentalIncomeAccountedForBySingleTenant
Namespace Prefix:	exr
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The number of real estate properties owned by franchisees and other third parties as of the balance sheet date.

Name:	exr_NumberOfRealEstatePropertiesFranchiseesAndOthers
Namespace Prefix:	exr
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of real estate properties owned and/or managed as of the balance sheet date.

Name:	exr_NumberOfRealEstatePropertiesOwnedAndOrManaged
Namespace Prefix:	exr
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of remaining development projects in process as of the balance sheet date.

Name:	exr_RealEstateRemainingDevelopmentProjectsInProcessNumber
Namespace Prefix:	exr
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of reportable segments of the entity.

Name:	exr_ReportingSegmentsNumber
Namespace Prefix:	exr
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of real estate properties owned as of the balance sheet date.

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of states the entity operates in as of the balance sheet date.

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Name:	us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration