NONCONTROLLING INTERESTS - Interests in Consolidated Real Estate Joint Ventures (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) facility	Dec. 31, 2022 USD ($)
Variable Interest Entity [Line Items]
Total assets	$ 6,233,225	$ 6,325,830
Total liabilities	$ 3,360,082	$ 3,428,030
VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	7
Total assets	$ 150,937
Total liabilities	82,616
Carrying amount of mortgage loans	$ 74,527
1074 Raritan Road, LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	90.00%
Total assets	$ 8,547
Total liabilities	$ 2,335
350 Main Street, LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	90.00%
Total assets	$ 5,311
Total liabilities	$ 64
Astoria Investors, LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	70.00%
Total assets	$ 38,105
Total liabilities	23,507
Carrying amount of mortgage loans	$ 18,603
CS Vienna LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	80.00%
Total assets	$ 31,050
Total liabilities	35,238
Carrying amount of mortgage loans	$ 34,875
CS Valley Forge Village Storage LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	70.00%
Total assets	$ 20,325
Total liabilities	15,594
Carrying amount of mortgage loans	$ 15,509
SH3, LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	90.00%
Total assets	$ 37,133
Total liabilities	$ 297
C S Lock Up Anoka LLC | VIE
Variable Interest Entity [Line Items]
Number of self-storage facilities owned and operated | facility	1
Ownership interest held by the entity (as a percent)	50.00%
Total assets	$ 10,466
Total liabilities	5,581
Carrying amount of mortgage loans	$ 5,540