ACQUISITIONS AND DISPOSITIONS - Carrying Value of Assets and Liabilities at Time of Sale and Held for Sale (Details)			1 Months Ended	3 Months Ended
	Mar. 14, 2019 USD ($)	Mar. 01, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2019 property	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Disposal Group
Ownership sold, percentage					100.00%
Assets
Total assets, net			$ 58,216,000		$ 58,216,000		$ 22,175,000
Liabilities
Total liabilities			41,861,000		41,861,000		28,766,000
Deferred loan costs			1,417,000		1,417,000
Debt, accumulated amortization			494,000		494,000
Payment of mortgages payable					46,000,000	$ 510,000
Impairment of real estate					66,200,000	$ 0
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Assets
Investments in real estate, net			270,910,000		270,910,000
Deferred rent receivable and charges, net			32,284,000		32,284,000
Other intangible assets, net			316,000		316,000
Total assets, net			303,510,000		303,510,000
Liabilities
Debt, net			278,777,000		278,777,000
Total liabilities			278,777,000		278,777,000
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Investments in real estate, net			48,253,000		48,253,000		17,123,000
Cash and cash equivalents			745,000		745,000		755,000
Accounts receivable, net			137,000		137,000		41,000
Deferred rent receivable and charges, net			8,743,000		8,743,000		4,009,000
Other intangible assets, net			0		0		220,000
Other assets			338,000		338,000		27,000
Total assets, net			58,216,000		58,216,000		22,175,000
Liabilities
Debt, net			39,292,000		39,292,000		28,018,000
Accounts payable and accrued expenses			1,592,000		1,592,000		370,000
Due to related parties			204,000		204,000		81,000
Other liabilities			773,000		773,000		297,000
Total liabilities			41,861,000		41,861,000		28,766,000
Deferred loan costs			287,000		287,000		243,000
Debt, accumulated amortization			79,000		79,000		61,000
Debt, gross			39,500,000		39,500,000		28,200,000
Investments in real estate			64,363,000		64,363,000		24,832,000
Investments in real estate, accumulated depreciation			16,110,000		16,110,000		7,709,000
Deferred rent receivable			5,650,000		5,650,000		2,909,000
Deferred leasing costs			4,370,000		4,370,000		1,669,000
Deferred leasing costs, accumulated amortization			1,277,000		1,277,000		569,000
Acquired In-Place Leases | Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Other intangible assets, net							1,778,000
Liabilities
Other intangible assets, accumulated amortization							$ 1,558,000
Office Property, San Fransisco California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Disposal Group
Outstanding amount	$ 28,200,000
Office Property, Washington, D.C. | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Payment of mortgages payable		$ 46,000,000
Office Property, Oakland California | Disposal Group, Held-for-sale, Not Discontinued Operations
Disposal Group
Contracted sales price			$ 115,430,000		$ 115,430,000
260 Townsend Street, San Francisco, CA
Disposal Group
Ownership sold, percentage			100.00%
Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026 | Disposal Group, Held-for-sale, Not Discontinued Operations
Disposal Group
Outstanding amount			$ 39,500,000
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		$ 205,500,000
Scenario, Forecast | Land and Building
Liabilities
Ownership percentage to be sold in potential sale				100.00%
Scenario, Forecast | Building
Liabilities
Number of real estate investment property sold in potential sale | property				2
Scenario, Forecast | Land
Liabilities
Number of real estate investment property sold in potential sale | property				1