SIGNIFICANT ACCOUNTING POLICIES (Schedule of Consolidated Statements of Cash Flows - Supplemental Disclosures) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Supplemental disclosure of cash flow information:
Interest paid					$ 4,851	$ 1,675
Supplemental disclosure of non-cash investing and financing activities:
Stock dividend paid on preferred stock	$ 2,125	$ 2,125	$ 2,125	$ 2,125	4,250	4,250
Dividends declared, but not paid, on preferred stock					5,245	5,094
Dividends declared, but not yet paid, on common stock					5,351	7,754
Dividends declared, but not paid, on OC Units					433	0
Reclassification of development property investments to self-storage real estate owned					205,153	8,351
Reclassification of other assets and liabilities to self-storage real estate owned					1,504	0
Other loans paid off with issuance of development property investments					0	247
Contingent consideration for Internalization					8,554	0
Property Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
OC Units issued for Internalization	5,157	1,536
Internalization [Member]
Supplemental disclosure of non-cash investing and financing activities:
OC Units issued for Internalization		42,092
Non-Controlling Interests [Member] | Property Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
OC Units issued for self-storage real estate owned acquisitions					6,693	0
OC Units issued for Internalization	$ 5,157	1,536
Non-Controlling Interests [Member] | Internalization [Member]
Supplemental disclosure of non-cash investing and financing activities:
OC Units issued for Internalization		$ 33,538			$ 33,538	$ 0