DEBT - Narrative (Details)											1 Months Ended		3 Months Ended		12 Months Ended
	May 01, 2020 USD ($)	May 16, 2019 USD ($) mortgage_loan	Mar. 14, 2019 USD ($) mortgage_loan	Mar. 11, 2019 USD ($) swap	Mar. 01, 2019 USD ($)	Feb. 28, 2019 USD ($)	Dec. 28, 2018 USD ($) swap	Oct. 30, 2018 USD ($)	May 30, 2018 USD ($)	Sep. 21, 2017 USD ($) mortgage_loan	Oct. 31, 2018 USD ($) extension	Jun. 30, 2016 USD ($) agreement	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($) swap	Aug. 13, 2015 USD ($)
Debt
Deferred loan costs													$ 4,535,000		$ 4,535,000
Deferred loan costs, accumulated amortization													1,760,000		1,494,000
Loss on early extinguishment of debt													0	$ 25,071,000
Payment of mortgages payable													0	46,000,000
Prepayment penalties and other payments for early extinguishment of debt													0	5,562,000
Restricted cash													10,430,000	11,738,000	12,146,000
Number of swaps terminated | swap				2			1									7
Notional amount of terminated swaps				$ 120,000,000			$ 50,000,000									$ 215,000,000
Accrued interest and unused commitment fee payable													671,000		650,000
Mortgages Payable
Debt
Number of mortgage loan agreements | agreement												6
Amount of loan												$ 392,000,000
Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026
Debt
Gross debt													$ 97,100,000		97,100,000
Fixed interest rate													4.14%
Loan Backed Notes
Debt
Proceeds from notes payable									$ 38,200,000
Weight average life									2 years
Restricted cash													$ 1,725,000		$ 3,306,000
Loan Backed Notes | LIBOR
Debt
Interest rate margin									1.40%
Loan Backed Notes | Prime Rate
Debt
Interest rate margin									1.08%
Revolving Credit Facility
Debt
Maximum borrowing capacity											$ 250,000,000
Interest rate													2.41%		3.29%
Number of extensions | extension											1
Extension option, term											1 year
Proceeds from issuance of debt								$ 170,000,000
Revolving Credit Facility | Minimum
Debt
Unused commitment fee percentage											0.15%
Revolving Credit Facility | Maximum
Debt
Unused commitment fee percentage											0.25%
Revolving Credit Facility | LIBOR
Debt
Interest rate margin											1.55%
Revolving Credit Facility | Base rate
Debt
Interest rate margin											0.55%
7083 Hollywood Boulevard, Los Angeles, California | Disposal Group, Held-for-sale, Not Discontinued Operations
Debt
Number of mortgage loans assumed by buyer | mortgage_loan										1
Outstanding amount										$ 21,700,000
Properties Used As Collateral For Loans | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026
Debt
Loss on early extinguishment of debt														19,290,000
Write off of deferred loan costs					$ 637,000
Write off of accumulated amortization					170,000
Transaction costs					237,000
Defeased amount					205,500,000
Cash outlay required for defeasance					224,086,000
Office Property, San Fransisco California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Debt
Number of mortgage loans assumed by buyer | mortgage_loan			1
Outstanding amount			$ 28,200,000
Loss on early extinguishment of debt														178,000
Write off of deferred loan costs														243,000
Write off of accumulated amortization														65,000
1333 Broadway, Oakland, CA | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mortgage loan with a fixed interest of 4.14% per annum, due on July 1, 2026
Debt
Loss on early extinguishment of debt															$ 4,911,000
Write off of deferred loan costs		$ 287,000
Write off of accumulated amortization		82,000
Transaction costs		98,000
Defeased amount		39,500,000
Cash outlay required for defeasance		$ 44,108,000
Number of mortgage loans defeased | mortgage_loan		1
Office Property, Washington, D.C. | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Debt
Loss on early extinguishment of debt														$ 5,603,000
Write off of deferred loan costs					537,000
Write off of accumulated amortization					259,000
Payment of mortgages payable					46,000,000
Prepayment penalties and other payments for early extinguishment of debt					$ 5,325,000
Interest Rate Swap
Debt
Total notional amount																	$ 385,000,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedges
Debt
Total notional amount													$ 120,000,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedges | Weighted Average
Debt
All-in rate													3.11%
Revolving Credit Facility | Line of Credit
Debt
Repayments of debt				$ 120,000,000		$ 10,000,000	$ 40,000,000
Gross debt													$ 159,500,000		153,000,000
Remaining borrowing capacity													$ 64,900,000		$ 73,900,000
Unsecured Revolving Credit Facility Due May 2022 | Revolving Credit Facility | Subsequent Event | Line of Credit
Debt
Maximum borrowing capacity	$ 10,000,000
Fixed interest rate	1.00%
Fee percentage for each advance made	1.12%
Maximum fee amount payable	$ 112,000