FAIR VALUE MEASUREMENTS - Financial Assets and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
FINANCIAL LIABILITIES
Unsecured senior notes	$ 319,286	$ 269,246
Mortgages payable	608,363
Carrying Amount
FINANCIAL ASSETS
Cash and cash equivalents	5,194	392
FINANCIAL LIABILITIES
Revolving lines of credit	87,000	152,871
Term loans	145,000	145,000
Unsecured senior notes	175,000	125,000
Mortgages payable	288,363	298,445
Carrying Amount | Restricted cash
FINANCIAL ASSETS
Cash and cash equivalents	8,444	6,918
Fair Value
FINANCIAL ASSETS
Cash and cash equivalents	5,194	392
FINANCIAL LIABILITIES
Revolving lines of credit	87,000	152,871
Term loans	145,000	145,000
Unsecured senior notes	183,259	133,181
Mortgages payable	297,683	308,855
Fair Value | Restricted cash
FINANCIAL ASSETS
Cash and cash equivalents	$ 8,444	$ 6,918