Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Parenthetical) (Detail) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020 USD ($) Property	Mar. 31, 2020 USD ($) Property	Nov. 30, 2019 USD ($) Property	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Property	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Property
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property						31
Gain on sale of storage facilities					$ 100,222		$ 100,222
Distributions from unconsolidated joint ventures						$ 9,246	7,419
Cash payment for property acquisition						417,930	354,712
Mortgages payable	$ 34,352					$ 34,352		$ 34,851
Ontario, Canada [Member]
Schedule of Equity Method Investments [Line Items]
Number of joint venture developing self-storage facilities | Property	2					2
New York City [Member]
Schedule of Equity Method Investments [Line Items]
Number of joint venture developing self-storage facilities | Property	3					3
Sovran HHF Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Excess of investment over net asset due to capitalization of acquisition related costs	$ 1,700					$ 1,700
Total consideration acquired	175,200
Settlement of principal balances with non-recourse loans	34,000
Gain on sale of storage facilities	$ 2,100
Sovran HHF Storage Holdings LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property	17
Sovran HHF Storage Holdings LLC [Member] | Storage Facilities [Member] | Third Party [Member]
Schedule of Equity Method Investments [Line Items]
Total consideration acquired	$ 42,300
Number of properties sold | Property	4
Sovran HHF Storage Holdings II LLC [Member]
Schedule of Equity Method Investments [Line Items]
Total consideration acquired	$ 120,200
Cash has been placed into escrow until non-recourse loans	35,800					35,800
Contribution of company to joint venture as share in capital	$ 12,700
Sovran HHF Storage Holdings II LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property	8
191 III Life Storage Holdings LLC [Member]
Schedule of Equity Method Investments [Line Items]
Payment for property acquisition		$ 124,200
Distributions from unconsolidated joint ventures		$ 8,400
191 III Life Storage Holdings LLC [Member] | Storage Facilities [Member] | California [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property		6
Life Storage-HIERS Storage LLC [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital								$ 5,700
Life Storage-HIERS Storage LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Number of storage facilities acquired | Property			5					5
Cash payment for property acquisition			$ 56,300
Mortgages payable			$ 27,600
Iskalo Office Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Rent paid during the period						900	$ 900
Bluebird Sanford Storage LP [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital								$ 300
Bluebird Sanford Storage LP [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Cash payment for property acquisition								4,900
Mortgages payable								3,200
Bluebird Ingram Storage LP [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital								1,300
Bluebird Ingram Storage LP [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Cash payment for property acquisition								20,700
Mortgages payable								17,600
Life Storage Spacemax, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital								16,300
Life Storage Spacemax, LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Cash payment for property acquisition								82,700
Mortgages payable								$ 42,000
Number of self-storage facilities | Property								6
Life Storage Virtus, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital						$ 1,700
Life Storage Virtus, LLC [Member] | Storage Facilities [Member]
Schedule of Equity Method Investments [Line Items]
Cash payment for property acquisition				$ 21,700
Mortgages payable		$ 14,000		$ 14,000
Joint Ventures with Properties in Development Stage [Member]
Schedule of Equity Method Investments [Line Items]
Number Of joint ventures | Property						5
Joint Ventures with Properties in Development Stage [Member] | Common Stock Shares [Member]
Schedule of Equity Method Investments [Line Items]
Contribution of company to joint venture as share in capital						$ 6,400