SELF STORAGE PROPERTY ACQUISITIONS AND DISPOSITIONS - Narrative (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2024 property	Sep. 30, 2024 property	Jun. 30, 2024 property	Mar. 31, 2024 property	Dec. 31, 2023 property	Sep. 30, 2023 property	Jun. 30, 2023 property	Mar. 31, 2023 property	Dec. 31, 2024 USD ($) property	Dec. 31, 2023 USD ($) property
Asset Acquisition [Line Items]
Number of properties acquired | property	4	0	3	0	2	2	0	16	7	20
Estimated fair value of net assets acquired									$ 64.9	$ 229.5
Acquisition-related costs capitalized									0.3	1.6
Aggregate revenue related to properties acquired during the year									1.5	12.3
Operating income related to properties acquired during the year									1.4	10.9
Undeveloped land parcel, net proceeds										262.3
Net gain of dispositions									63.8	$ 63.9
Self storage property disposed | property										32
Real Estate
Asset Acquisition [Line Items]
Recognized fair value allocated to real estate									63.5	$ 224.7
Customer in-place leases
Asset Acquisition [Line Items]
Recognized fair value allocated to intangible assets									$ 1.4	$ 4.8
Third Party
Asset Acquisition [Line Items]
Number of self storage properties, disposition | property									40
Undeveloped land parcel, net proceeds									$ 273.1
Joint Venture
Asset Acquisition [Line Items]
Number of self storage properties, disposition | property									56
Undeveloped land parcel, net proceeds									$ 343.7
Asset acquired from PROs | Affiliated entity
Asset Acquisition [Line Items]
Number of properties acquired | property										19
Estimated fair value of net assets acquired										$ 199.3