Investments in Unconsolidated Real Estate Entities - Schedule of Investments in Unconsolidated Real Estate Ventures (Details) $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Oct. 31, 2019 USD ($)	Jan. 31, 2019 USD ($) store	Dec. 31, 2019 USD ($) store property	Sep. 30, 2019 USD ($) store	Jun. 30, 2019 USD ($) store	Mar. 31, 2019 USD ($) store	Dec. 31, 2018 USD ($) store	Sep. 30, 2018 USD ($) store	Jun. 30, 2018 USD ($) store	Mar. 31, 2018 USD ($) store	Dec. 31, 2019 USD ($) store property	Dec. 31, 2018 USD ($) store	Dec. 31, 2017 USD ($)	Nov. 30, 2017
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			241								241
Investment balance			$ 292,790				$ 80,129				$ 292,790	$ 80,129
Amount invested											$ 197,759	$ 65,500	$ 17,944
Number of stores acquired | store			5	1	1	14	6	6	17	5	21	34
Cash paid to acquire properties			$ 51,058	$ 16,941	$ 8,424	$ 202,890	$ 74,868	$ 71,989	$ 148,650	$ 70,171	$ 279,313	$ 365,678
Minimum
Schedule of Equity Method Investments [Line Items]
Equity Ownership %			10.00%				10.00%				10.00%	10.00%	10.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Equity Ownership %			50.00%				50.00%				50.00%	50.00%	25.00%
PRISA Self Storage LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			85								85
Equity Ownership %			4.00%								4.00%
Excess Profit %			4.00%								4.00%
Investment balance			$ 9,133				$ 9,334				$ 9,133	$ 9,334
Storage Portfolio II JV LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			36								36
Equity Ownership %			10.00%								10.00%			10.00%
Excess Profit %			30.00%								30.00%
Investment balance			$ (4,827)				(4,233)				$ (4,827)	(4,233)
Storage Portfolio I LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			24								24
Equity Ownership %			34.00%								34.00%
Excess Profit %			49.00%								49.00%
Investment balance			$ (38,345)				(38,129)				$ (38,345)	(38,129)
VRS Self Storage, LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			16								16
Equity Ownership %			45.00%								45.00%
Excess Profit %			54.00%								54.00%
Investment balance			$ 17,639				18,281				$ 17,639	18,281
ESS-NYFL JV LP
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			11								11
Equity Ownership %			16.00%								16.00%
Excess Profit %			24.00%								24.00%
Investment balance			$ 13,320				0				$ 13,320	0
WICNN JV LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			10								10
Equity Ownership %			10.00%								10.00%
Excess Profit %			25.00%								25.00%
Investment balance			$ 36,552				26,885				$ 36,552	26,885
Joint venture preferred equity investment			$ 31,500								$ 31,500
Joint venture preferred equity investment return percentage											8.00%
Extra Space Northern Properties Six LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			10								10
Equity Ownership %			10.00%								10.00%
Excess Profit %			35.00%								35.00%
Investment balance			$ (2,091)				(1,700)				$ (2,091)	(1,700)
Alan Jathoo JV LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			9								9
Equity Ownership %			10.00%								10.00%
Excess Profit %			10.00%								10.00%
Investment balance			$ 7,977				8,180				$ 7,977	8,180
PR EXR Self Storage, LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			5								5
Equity Ownership %			25.00%								25.00%
Excess Profit %			40.00%								40.00%
Investment balance			$ 59,391				19,841				$ 59,391	19,841
ESS Bristol Investments LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			8								8
Equity Ownership %			10.00%								10.00%
Excess Profit %			28.00%								28.00%
Investment balance			$ 3,046				2,331				$ 3,046	2,331
GFN JV, LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			5								5
Equity Ownership %			10.00%								10.00%
Excess Profit %			30.00%								30.00%
Investment balance			$ 12,168				10,586				$ 12,168	10,586
Joint venture preferred equity investment			$ 10,335								$ 10,335
Joint venture preferred equity investment return percentage											8.00%
Extra Space West Two LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			0								0
Equity Ownership %			5.00%								5.00%
Excess Profit %			40.00%								40.00%
Investment balance			$ 0				3,818				$ 0	3,818
Extra Space West One LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			0								0
Equity Ownership %			5.00%								5.00%
Excess Profit %			40.00%								40.00%
Investment balance			$ 0				(1,038)				$ 0	(1,038)
Other minority owned stores
Schedule of Equity Method Investments [Line Items]
Number of Stores | property			22								22
Investment balance			$ 28,827				25,973				$ 28,827	25,973
Other minority owned stores | Minimum
Schedule of Equity Method Investments [Line Items]
Equity Ownership %			10.00%								10.00%
Excess Profit %			19.00%								19.00%
Other minority owned stores | Maximum
Schedule of Equity Method Investments [Line Items]
Equity Ownership %			50.00%								50.00%
Excess Profit %			50.00%								50.00%
SmartStop Self Storage REIT, Inc. Preferred Stock
Schedule of Equity Method Investments [Line Items]
Investment balance			$ 150,000				$ 0				$ 150,000	$ 0
Amount invested	$ 150,000
Investment commitment	$ 50,000
Investment commitment, period	12 months
Investment, preferred dividend rate	6.25%
Period after which preferred stock dividend is subject to increase	5 years
Period after which preferred stock dividend is redeemable	5 years
Extra Space West One and Two LLC
Schedule of Equity Method Investments [Line Items]
Equity Ownership %		100.00%
Number of stores acquired | store		12
Cash paid to acquire properties		$ 172,505