Lines of Credit - Summarized Information of Lines of Credit (Detail) (USD $)	12 Months Ended
Dec. 31, 2014
Line of Credit Facility [Line Items]
Amount drawn	$ 138,000,000us-gaap_LineOfCredit
Capacity	265,000,000
Credit Line 1 [Member]
Line of Credit Facility [Line Items]
Amount drawn	7,000,000
Capacity	85,000,000
Interest rate	2.10%
Origination date	Jun. 04, 2010
Maturity	Jun. 03, 2016
Line of credit facility variable rate basis	LIBOR
Basis spread on variable rate	1.90%
Credit Line 2 [Member]
Line of Credit Facility [Line Items]
Amount drawn	41,000,000
Capacity	50,000,000
Interest rate	1.90%
Origination date	Nov. 16, 2010
Maturity	Feb. 13, 2017
Line of credit facility variable rate basis	LIBOR
Basis spread on variable rate	1.80%
Credit Line 3 [Member]
Line of Credit Facility [Line Items]
Amount drawn	50,000,000
Capacity	80,000,000
Interest rate	1.90%
Origination date	Apr. 29, 2011
Maturity	Nov. 18, 2016
Line of credit facility variable rate basis	LIBOR
Basis spread on variable rate	1.70%
Credit Line 4 [Member]
Line of Credit Facility [Line Items]
Amount drawn	40,000,000
Capacity	$ 50,000,000
Interest rate	1.80%
Origination date	Sep. 29, 2014
Maturity	Sep. 29, 2017
Line of credit facility variable rate basis	LIBOR
Basis spread on variable rate	1.70%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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

- Definition

Date the credit facility first became available, in CCYY-MM-DD format.

+ References

+ Details

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

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
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- Details

Name:	us-gaap_LineOfCreditFacilityLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

Name:	us-gaap_LineOfCreditFacilityAxis=exr_SecondCreditLineMember
Namespace Prefix:
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- Details

Name:	us-gaap_LineOfCreditFacilityAxis=exr_ThirdCreditLineMember
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