Property Acquisitions and Dispositions - Acquisitions of Operating Stores (Details)				3 Months Ended								12 Months Ended
	Nov. 17, 2016 USD ($) store	Sep. 16, 2016 USD ($) store	Feb. 02, 2016 USD ($) store	Dec. 31, 2017 USD ($) store shares	Sep. 30, 2017 USD ($) store shares	Jun. 30, 2017 USD ($) store shares	Mar. 31, 2017 USD ($) store shares	Dec. 31, 2016 USD ($) store shares	Sep. 30, 2016 USD ($) store shares	Jun. 30, 2016 USD ($) store shares	Mar. 31, 2016 USD ($) store shares	Dec. 31, 2017 USD ($) store shares	Dec. 31, 2016 USD ($) store shares	Dec. 31, 2015
Business Acquisition [Line Items]
Number of stores | store				37	4	3	2	27	27	22	23	46	99
Total				$ 535,299,000	$ 31,966,000	$ 34,641,000	$ 25,556,000	$ 320,564,000	$ 296,280,000	$ 244,264,000	$ 225,537,000	$ 627,462,000	$ 1,086,645,000
Cash Paid				502,845,000	29,919,000	16,608,000	25,541,000	297,569,000	296,345,000	176,689,000	225,156,000	574,913,000	995,759,000
Loan Assumed				14,592,000	0	9,463,000	0	0	0	9,723,000	0	24,055,000	9,723,000
Non- controlling Interests				(1,812,000)	0	1,827,000	0	0	0	0	0	15,000	0
Investments in Real Estate Ventures				12,957,000	0	0	0	0	0	0	0	12,957,000	0
Net Liabilities/ (Assets) Assumed				1,099,000	47,000	(67,000)	15,000	4,997,000	(65,000)	1,615,000	381,000	1,094,000	6,928,000
Value of OP Units Issued				$ 5,618,000	$ 2,000,000	$ 6,810,000	$ 0	$ 17,998,000	$ 0	$ 56,237,000	$ 0	$ 14,428,000	$ 74,235,000
Number of OP Units Issued (in shares) | shares				64,708	25,520	272,400	0	563,819	0	2,215,231	0	362,628	2,779,050
Real Estate Assets				$ 535,299,000	$ 31,966,000	$ 34,641,000	$ 25,556,000	$ 328,683,000	$ 307,268,000	$ 244,264,000	$ 269,721,000	$ 627,462,000	$ 1,149,936,000
Number of acquired stores | store				7
Gain (loss) on sale of properties				$ 0
Equity method ownership percentage				25.00%								25.00%		50.00%
ESS PRISA II LLC Joint Venture
Business Acquisition [Line Items]
Number of acquired stores | store		23
Equity method ownership percentage		4.40%
Number of stores owned | store								42
Extra Space Properties One Three One LLC
Business Acquisition [Line Items]
Net carrying amount of properties distributed		$ 4,326,000
Equity Ownership (as a percent)		100.00%
Previous equity interest		$ 10,988,000
Step acquisition, equity interest in acquiree, remeasurement gain		$ 6,778,000
Number of transferred stores | store		23
VRS
Business Acquisition [Line Items]
Number of acquired stores | store			6
Equity method ownership percentage			45.00%
Extra Space Properties One Two Two LLC
Business Acquisition [Line Items]
Fair value of real estate assets acquired			$ 98,082,000
Number of acquired stores | store			6
Net carrying amount of properties distributed			$ 17,261,000
Equity Ownership (as a percent)			100.00%
Previous equity interest			$ 44,184,000
Step acquisition, equity interest in acquiree, remeasurement gain			$ 26,923,000
Number of transferred stores | store			6
ESS WCOT LLC Joint Venture
Business Acquisition [Line Items]
Fair value of real estate assets acquired	$ 161,072,000
Number of acquired stores | store	11
Equity method ownership percentage	5.00%
Additional interest acquired in the venture	94.96%
Net carrying amount of properties distributed	$ 68,814,000
Amount paid to acquire joint venture partners interests	$ 153,304,000
Equity Ownership (as a percent)	100.00%
Previous equity interest	$ 8,119,000
Step acquisition, equity interest in acquiree, remeasurement gain	$ 4,651,000
Prudential Real Estate and Affiliates | ESS PRISA II LLC Joint Venture
Business Acquisition [Line Items]
Additional interest acquired in the venture		95.60%
Prudential Real Estate and Affiliates | Extra Space Properties One Three One LLC
Business Acquisition [Line Items]
Additional interest acquired in the venture		95.60%
Amount paid to acquire joint venture partners interests		$ 238,679,000
Prudential Real Estate and Affiliates | VRS
Business Acquisition [Line Items]
Additional interest acquired in the venture			55.00%
Prudential Real Estate and Affiliates | Extra Space Properties One Two Two LLC
Business Acquisition [Line Items]
Additional interest acquired in the venture			55.00%
Amount paid to acquire joint venture partners interests			$ 53,940,000
Various States Properties Sept16, 2016
Business Acquisition [Line Items]
Fair value of real estate assets acquired		$ 248,530,000