Investments in Unconsolidated Real Estate Ventures - Schedule of Investments (Details) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended
	Jan. 31, 2019 USD ($) store	Sep. 30, 2019 USD ($) store property	Jun. 30, 2019 USD ($) store	Mar. 31, 2019 USD ($) store	Sep. 30, 2018 USD ($) store	Jun. 30, 2018 USD ($) store	Mar. 31, 2018 USD ($) store	Sep. 30, 2019 USD ($) store property	Sep. 30, 2018 USD ($) store	May 31, 2019	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of Stores | property		242						242
Investment balance		$ 130,299						$ 130,299			$ 80,129
Number of stores acquired | store		1	1	14	6	17	5	16	28
Cash paid		$ 16,941	$ 8,424	$ 202,890	$ 71,989	$ 148,650	$ 70,171	$ 228,255	$ 290,810
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		$ 9,182						$ 9,182			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%
Excess Profit %		30.00%						30.00%
Investment balance		$ (4,754)						$ (4,754)			(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		$ (38,406)						$ (38,406)			(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		$ 17,560						$ 17,560			18,281
ESS-NYFL JV LP
Schedule of Equity Method Investments [Line Items]
Number of Stores | property		15						15
Equity Ownership %		16.00%						16.00%		16.00%
Excess Profit %		24.00%						24.00%
Investment balance		$ 13,931						$ 13,931			0
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		$ (1,969)						$ (1,969)			(1,700)
WICNN JV LLC
Schedule of Equity Method Investments [Line Items]
Number of Stores | property		9						9
Equity Ownership %		10.00%						10.00%
Excess Profit %		25.00%						25.00%
Investment balance		$ 32,428						$ 32,428			26,885
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		$ 8,021						$ 8,021			8,180
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		$ 3,065						$ 3,065			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 %		25.00%						25.00%
Investment balance		$ 12,238						$ 12,238			10,586
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						$ 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						$ 0			(1,038)
Other minority owned stores
Schedule of Equity Method Investments [Line Items]
Number of Stores | property		25						25
Investment balance		$ 79,003						$ 79,003			$ 45,814
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%
Extra Space West One and Two LLC
Schedule of Equity Method Investments [Line Items]
Equity Ownership %	100.00%
Percentage interest purchased	95.00%
Number of stores acquired | store	12
Cash paid	$ 172,505