ACQUISITIONS AND DISPOSITIONS - Carrying Value of Assets and Liabilities at Time of Sale (Details) - USD ($) $ in Thousands			6 Months Ended
	Mar. 14, 2019	Mar. 01, 2019	Jun. 30, 2020	Jun. 30, 2019	May 16, 2019
Liabilities
Deferred loan costs				$ 1,704
Debt, accumulated amortization				576
Payment of mortgages payable			$ 0	46,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Assets
Investments in real estate, net				318,918
Deferred rent receivable and charges, net				41,280
Other intangible assets, net				316
Total assets				360,514
Liabilities
Debt, net				318,072
Total liabilities				$ 318,072
Office Property, San Fransisco California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Outstanding amount	$ 28,200
Office Property, Washington, D.C. | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Payment of mortgages payable		$ 46,000
Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026 | Properties Used As Collateral For Loans | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Defeased amount		$ 205,500
Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026 | 1333 Broadway, Oakland, CA | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Defeased amount					$ 39,500