DEBT - Narrative (Details)											1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	May 01, 2020 USD ($)	May 16, 2019 USD ($) mortgageLoan	Mar. 14, 2019 USD ($) mortgageLoan	Mar. 11, 2019 USD ($) swap	Mar. 01, 2019 USD ($)	Feb. 28, 2019 USD ($)	Dec. 28, 2018 USD ($) swap	Oct. 30, 2018 USD ($)	May 30, 2018 USD ($)	Sep. 21, 2017 USD ($) mortgageLoan	Oct. 31, 2018 USD ($) extensionOption	Jun. 30, 2016 USD ($) agreement	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($) swap	Dec. 31, 2017 USD ($) swap	Dec. 31, 2019 USD ($)	Aug. 13, 2015 USD ($)
Debt Instrument [Line Items]
Deferred loan costs													$ 4,770,000		$ 4,770,000			$ 4,535,000
Deferred loan costs, accumulated amortization													2,042,000		2,042,000			1,494,000
Loss on early extinguishment of debt													0	$ 4,911,000	0	$ 29,982,000
Payment of mortgages payable															0	46,000,000
Prepayment penalties and other payments for early extinguishment of debt															0	5,660,000
Restricted cash													10,960,000	10,824,000	10,960,000	$ 10,824,000		12,146,000
Number of swaps terminated | swap				2			1									2	7
Notional amount of terminated swaps				$ 120,000,000			$ 50,000,000										$ 215,000,000
Accrued interest and unused commitment fee payable													604,000		604,000			650,000
Mortgages Payable
Debt Instrument [Line Items]
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 Instrument [Line Items]
Gross debt													$ 97,100,000		$ 97,100,000			97,100,000
Fixed interest rate													4.14%		4.14%
Loan Backed Notes
Debt Instrument [Line Items]
Proceeds from notes payable									$ 38,200,000
Weight average life									2 years
Restricted cash													$ 2,330,000		$ 2,330,000			$ 3,306,000
Loan Backed Notes | LIBOR
Debt Instrument [Line Items]
Interest rate margin									1.40%
Loan Backed Notes | Prime Rate
Debt Instrument [Line Items]
Interest rate margin									(1.08%)
2018 Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 250,000,000
Interest rate													1.80%		1.80%			3.29%
Number of extension options | extensionOption											1
Extension option, term											1 year
Proceeds from issuance of debt								$ 170,000,000
2018 Revolving Credit Facility | Minimum
Debt Instrument [Line Items]
Unused commitment fee percentage											0.15%
2018 Revolving Credit Facility | Maximum
Debt Instrument [Line Items]
Unused commitment fee percentage											0.25%
2018 Revolving Credit Facility | LIBOR
Debt Instrument [Line Items]
Interest rate margin											1.55%
2018 Revolving Credit Facility | Base rate
Debt Instrument [Line Items]
Interest rate margin											0.55%
7083 Hollywood Boulevard, Los Angeles, California | Disposal Group, Held-for-sale, Not Discontinued Operations
Debt Instrument [Line Items]
Number of mortgage loans assumed by buyer | mortgageLoan										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 Instrument [Line Items]
Defeased amount					$ 205,500,000
Cash outlay required for defeasance					224,086,000
Loss on early extinguishment of debt														0		$ 19,290,000
Write off of deferred loan costs					637,000
Write off of accumulated amortization					170,000
Transaction costs					237,000
Office Property, San Fransisco California | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Debt Instrument [Line Items]
Number of mortgage loans assumed by buyer | mortgageLoan			1
Outstanding amount			$ 28,200,000
Loss on early extinguishment of debt														0		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 Instrument [Line Items]
Defeased amount		$ 39,500,000
Cash outlay required for defeasance		44,108,000
Loss on early extinguishment of debt														4,911,000		4,911,000
Write off of deferred loan costs		287,000
Write off of accumulated amortization		82,000
Transaction costs		$ 98,000
Number of mortgage loans defeased | mortgageLoan		1
Office Property, Washington, D.C. | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Debt Instrument [Line Items]
Loss on early extinguishment of debt														$ 0		$ 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 Instrument [Line Items]
Total notional amount																			$ 385,000,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedges
Debt Instrument [Line Items]
Total notional amount													$ 120,000,000		$ 120,000,000
Interest Rate Swap | Designated as Hedging Instrument | Cash Flow Hedges | Weighted Average
Debt Instrument [Line Items]
All-in rate													3.11%		3.11%
2018 Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Repayments of debt				$ 120,000,000		$ 10,000,000	$ 40,000,000
Gross debt													$ 209,500,000		$ 209,500,000			$ 153,000,000
Remaining borrowing capacity													0		0			73,900,000
Unsecured Revolving Credit Facility Due May 2022 | 2018 Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
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
Debt outstanding													0		0
Remaining borrowing capacity													10,000,000		10,000,000
Paycheck Protection Program Liquidity Facility, CARES Act | 2018 Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Gross debt													15,466,000		15,466,000			$ 0
Debt outstanding													$ 15,466,000		$ 15,466,000