SEGMENT REPORTING - Capital Expenditures (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Capital expenditures	[1]	$ 23,980	$ 13,383	$ 74,441	$ 36,793
Retail
Segment Reporting Information [Line Items]
Capital expenditures	[1]	5,290	3,221	16,731	8,678
Office
Segment Reporting Information [Line Items]
Capital expenditures	[1]	16,548	9,407	50,449	24,293
Multifamily
Segment Reporting Information [Line Items]
Capital expenditures	[1]	1,297	536	2,753	3,020
Mixed-use
Segment Reporting Information [Line Items]
Capital expenditures	[1]	$ 845	$ 219	$ 4,508	$ 802

[1] Capital expenditures represent cash paid for capital expenditures during the period and include leasing commissions paid