Variable Interests - Additional Information (Detail)	Jun. 30, 2018 joint_venture subsidiary
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of wholly-owned unconsolidated subsidiaries \| subsidiary	3
Number of interests in consolidated VIE joint ventures \| joint_venture	0

Represents the number of consolidated joint ventures that were variable interest entities.

No definition available.

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