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Fair Value Disclosures - Additional Information (Detail)	Mar. 31, 2018 store
Fair Value Disclosures [Abstract]
Number of operating stores held for sale	1

X

- Definition

Number of Operating Stores Owned Held-For-Sale

+ References

No definition available.

+ Details

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

X

- References

No definition available.

+ Details

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