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Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Thousands					1 Months Ended	3 Months Ended
	May 05, 2021 USD ($) Property	May 03, 2021 USD ($) Property	Apr. 26, 2021 USD ($)	Apr. 01, 2021 USD ($) $ / shares	Apr. 30, 2021 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) Property	Mar. 31, 2020 USD ($) Property	Dec. 31, 2020 USD ($)
Subsequent Event [Line Items]
Mortgages payable						$ 37,596		$ 37,777
Distributions from unconsolidated joint ventures						$ 2,547	$ 3,611
Number of storage facilities acquired \| Property						16	6
Aggregate purchase price						$ 266,215
Self-storage Facilities [Member]
Subsequent Event [Line Items]
Number of storage facilities acquired \| Property						6
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declared, date				Apr. 01, 2021
Dividend per common share \| $ / shares				$ 0.74
Dividend paid, date				Apr. 26, 2021
Dividend record, date				Apr. 14, 2021
Dividend paid			$ 56,900
Subsequent Event [Member] \| Equity Program [Member]
Subsequent Event [Line Items]
Common stock shares issued under equity offering program \| shares					377,621
Weighted average issue price \| $ / shares					$ 88.17
Proceeds from issuance of common stock					$ 33,000
Subsequent Event [Member] \| Self-storage Facilities [Member]
Subsequent Event [Line Items]
Number of storage facilities acquired \| Property	11	1
Aggregate purchase price	$ 159,200	$ 16,500
Subsequent Event [Member] \| Sovran HHF Storage Holdings II LLC [Member]
Subsequent Event [Line Items]
Mortgage debt paid off				$ 69,100
Mortgages payable				$ 110,000
Mortgage debt maturity year				2029
Distributions from unconsolidated joint ventures				$ 31,600