Investments in Unconsolidated Real Estate Ventures - Schedule of Investments in Unconsolidated Real Estate Ventures (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) property	Dec. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Investment balance	$ 63,868	$ 75,907
VRS Self Storage, LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	16
Equity method ownership percentage	45.00%
Excess profit participation percentage	54.00%
Investment balance	$ 18,930	19,467
PRISA Self Storage LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	85
Equity method ownership percentage	4.00%
Excess profit participation percentage	4.00%
Investment balance	$ 9,512	9,638
Extra Space West Two LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	5
Equity method ownership percentage	5.00%
Excess profit participation percentage	40.00%
Investment balance	$ 3,857	3,939
Extra Space West One LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	7
Equity method ownership percentage	5.00%
Excess profit participation percentage	40.00%
Investment balance	$ (936)	(900)
WCOT Self Storage LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	15
Equity method ownership percentage	5.00%
Excess profit participation percentage	20.00%
Investment balance	$ (992)	(357)
Extra Space Northern Properties Six LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	10
Equity method ownership percentage	10.00%
Excess profit participation percentage	35.00%
Investment balance	$ (1,388)	(1,279)
Storage Portfolio II JV LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	36
Equity method ownership percentage	10.00%
Excess profit participation percentage	30.00%
Investment balance	$ (3,278)	(3,140)
Storage Portfolio I LLC
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	24
Equity method ownership percentage	34.00%
Excess profit participation percentage	49.00%
Investment balance	$ (36,528)	11,495
Other minority owned stores
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	16
Investment balance	$ 31,418	31,228
Other minority owned stores \| Minimum
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	10.00%
Excess profit participation percentage	19.00%
Other minority owned stores \| Maximum
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage	50.00%
Excess profit participation percentage	50.00%
Net investments in and Cash distributions in unconsolidated real estate ventures
Schedule of Equity Method Investments [Line Items]
Number of Properties \| property	214
Investment balance	$ 20,595	$ 70,091

Equity Method Investment, Number Of Properties

No definition available.

Name:	exr_EquityMethodInvestmentNumberOfProperties
Namespace Prefix:	exr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of excess profit participation in unconsolidated joint ventures.

+ References

No definition available.

+ Details

Name:	exr_UnconsolidatedJointVenturesExcessProfitParticipationPercentage
Namespace Prefix:	exr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying amount of investments in unconsolidated real estate and other joint ventures not separately presented. This includes direct and indirect investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_RealEstateInvestmentsUnconsolidatedRealEstateAndOtherJointVentures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_VRSSelfStorageLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_StoragePortfolioILLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_StoragePortfolioIIJVLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_PRISASelfStorageLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_ExtraSpaceWestTwoLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_WCOTSelfStorageLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_ExtraSpaceWestOneLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_ExtraSpaceNorthernPropertiesSixLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_OtherMinorityOwnedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=exr_TotalInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: