ASSETS HELD FOR SALE AND DISCONTINUED OPERATIONS - Income Statement Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations	$ 10,636	$ 1,984	$ 304	$ (414)	$ (1,672)	$ (1,898)	$ (2,064)	$ (2,253)	$ 12,510	$ (7,887)	$ (10,027)
Asset Sale Transaction | Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rental revenues									250,715	241,299	223,358
Rental expenses									(66,476)	(63,670)	(58,053)
Real estate-related depreciation and amortization									(96,402)	(111,868)	(111,619)
Asset management fees, related party									(23,194)	(23,247)	(21,963)
Interest expense									(52,133)	(50,401)	(41,750)
Income (loss) from discontinued operations									12,510	(7,887)	(10,027)
Straight-line rent and amortization of above- and below-market leases									(6,279)	(9,922)	(12,118)
Capital expenditures and development activities									$ (47,745)	$ (43,916)	$ (43,236)