ACQUISITIONS AND DISPOSITIONS - Carrying Value of Assets and Liabilities at Time of Sale and Held for Sale (Details) - USD ($) $ in Thousands			12 Months Ended
	Mar. 14, 2019	Mar. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 16, 2019
Assets
Total assets, net			$ 0	$ 22,175
Liabilities
Total liabilities			0	28,766
Deferred loan costs			1,704
Debt, accumulated amortization			576
Payment of mortgages payable			46,000	0	$ 65,877
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Assets
Investments in real estate, net			476,532	0	631,740
Deferred rent receivable and charges, net			55,297	0	34,071
Other intangible assets, net			316	0	11,283
Other assets			4,096	0	38
Total assets, net			536,241	0	677,132
Liabilities
Debt, net			318,072	0	115,037
Other liabilities			0	0	14,029
Intangible liabilities, net			0	0	1,800
Total liabilities			$ 318,072	0	130,866
Premium on assumed mortgage					665
Debt assumed by buyers					$ 50,260
Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Investments in real estate, net				17,123
Cash and cash equivalents				755
Accounts receivable, net				41
Deferred rent receivable and charges, net				4,009
Other intangible assets, net				220
Other assets				27
Total assets, net				22,175
Liabilities
Debt, net				28,018
Accounts payable and accrued expenses				370
Due to related parties				81
Other liabilities				297
Total liabilities				28,766
Deferred loan costs				243
Debt, accumulated amortization				61
Investments in real estate				24,832
Investments in real estate, accumulated depreciation				7,709
Deferred rent receivable				2,909
Deferred leasing costs				1,669
Deferred leasing cost, accumulated amortization				569
Debt, gross				28,200
Acquired in-place Leases | Disposal Group, Held-for-sale, Not Discontinued Operations
Assets
Other intangible assets, net				1,778
Liabilities
Other intangible assets, accumulated amortization				$ 1,558
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 Loan4.14 Percent Due On1 July2026 | Properties Used As Collateral For Loans | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Defeased amount		$ 205,500				$ 39,500
Mortgage Loan4.14 Percent Due On1 July2026 | 1333 Broadway, Oakland, CA | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Liabilities
Defeased amount						$ 39,500