EQUITY AND MEZZANINE EQUITY - Additional Information (Details)		3 Months Ended		6 Months Ended
	Feb. 26, 2019 $ / shares shares	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Noncontrolling interests - operating partnership (in shares)		881,000		881,000		977,000
Common stock outstanding (in shares)		14,045,000		14,045,000		13,027,000
Sale of common shares, net | $		$ 54,574,000	$ 44,789,000	$ 66,356,000	$ 48,141,000
Preferred shares of beneficial interest, shares outstanding (in shares)		3,900,000		3,900,000		3,900,000
Preferred shares, annual distribution accrual rate (in dollars per share) | $ / shares				$ 1.65625
Preferred shares, dividend rate				6.625%
Preferred shares liquidation preference | $		$ 97,000,000.0		$ 97,000,000.0
Units converted, ratio	1.37931
Conversion price (in dollars per share) | $ / shares	$ 72.50
Series D Preferred Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred units, shares issued (in shares)	165,600	166,000		166,000		166,000
Preferred units, par value (in dollars per share) | $ / shares	$ 100	$ 100		$ 100		$ 100
Distribution rate	3.862%
Series C Preferred Shares Of Beneficial Interest
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred shares of beneficial interest, shares outstanding (in shares)		3,881,000		3,881,000		3,881,000
Preferred shares, liquidation preference (in dollars per share) | $ / shares		$ 25.00		$ 25.00		$ 25
Preferred shares liquidation preference | $		$ 97,036,000		$ 97,036,000		$ 97,036,000
At-The-Market Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate gross sales price of common shares | $		$ 99,000		$ 99,000			$ 150,000,000.0
2015 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards issued (in shares)		23,385	19,508	26,186	20,701
Sale of common shares, net | $		$ 750,000	$ 956,000	$ 914,000	$ 1,000,000.0