INVESTMENT IN UNCONSOLIDATED JOINT VENTURES (Investments - Narrative) (Details)		3 Months Ended		6 Months Ended		12 Months Ended
	May 18, 2012 USD ($)	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jun. 27, 2019 USD ($) unit	May 02, 2014 ft²
Schedule of Equity Method Investments [Line Items]
Contributions to joint venture				$ 5,000,000	$ 1,320,000
Income from unconsolidated joint venture		$ 0	$ 131,000	$ 0	185,000
Rentable square feet | ft²		3,400,000		3,400,000
Investments in unconsolidated joint ventures		$ 51,956,000		$ 51,956,000		$ 44,869,000
Equity in (income) loss of unconsolidated joint ventures, net		215,000	2,373,000	(7,096,000)	4,751,000
110 William JV Partner
Schedule of Equity Method Investments [Line Items]
Income from unconsolidated joint venture				5,200,000
NIP Joint Venture
Schedule of Equity Method Investments [Line Items]
Contributions to joint venture	$ 8,000,000
Distributions		300,000	900,000	300,000	1,300,000
Income from unconsolidated joint venture			100,000		200,000
Return of capital		300,000	800,000		1,100,000
Investments in unconsolidated joint ventures		$ 1,225,000		$ 1,225,000		1,476,000
NIP Joint Venture | Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage		5.00%		5.00%
110 William Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership percentage		60.00%		60.00%
Distributions					$ 0
Income from unconsolidated joint venture				$ 7,800,000
Rentable square feet | ft²								928,157
Area of land | ft²								0.8
Investments in unconsolidated joint ventures		$ 0		0		325,000
Capitalized acquisition costs						1,400,000
Equity in (income) loss of unconsolidated joint ventures, net			$ 1,500,000			3,100,000
Equity in income of unconsolidated joint venture				7,500,000
Company’s equity in income (loss) of unconsolidated joint venture				7,800,000
Loss from equity method investments		0		300,000
110 William Joint Venture | 110 William JV Partner
Schedule of Equity Method Investments [Line Items]
Ownership percentage								60.00%
Noncontrolling interest								40.00%
Pacific Oak Opportunity Zone Fund I
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated joint ventures		5,050,000		5,050,000		$ 0
Investments		5,100,000		$ 5,100,000			$ 5,000,000
Number of units in real estate property | unit							22
Acquisition related costs		$ 100,000