Summary of Significant Accounting Policies - Variable Interest Entities (Details)	Dec. 31, 2017 entity
Accounting Policies [Abstract]
Number of nonconsolidated VIEs to which Operating Partnership has notes payable (in number of entities)	3

The number of Variable Interest Entities (VIE) which are not included in the consolidated financial statements of the entity because the entity does not have a controlling financial interest (not the primary beneficiary).

No definition available.

Name:	exr_VariableInterestEntityNotPrimaryBeneficiaryNumberAndNotConsolidatedNumber
Namespace Prefix:	exr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant