REAL ESTATE AND RELATED LEASE INTANGIBLES, NET - Pro forma (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate [Line Items]
Operating lease income									$ 89,492	$ 77,277	$ 80,465
Net income (loss)	$ 45,370	$ 29,821	$ 31,058	$ 19,630					125,879	113,720	146,134
Net (income) loss attributable to noncontrolling interest in consolidated joint ventures										138	(1,568)
Net (income) loss attributable to noncontrolling interest in operating partnership	(9,172)	(6,499)	(8,868)	(5,838)	$ (29,467)	$ (22,429)	$ (908)	$ 5,673	(30,377)	(47,131)	(70,745)
Acquisitions
Real Estate [Line Items]
Operating lease income										2,473	10,966
Net income (loss)										2,080	7,363
Net (income) loss attributable to noncontrolling interest in consolidated joint ventures										0	0
Net (income) loss attributable to noncontrolling interest in operating partnership										(865)	(3,334)
Consolidated Pro Forma
Real Estate [Line Items]
Operating lease income										79,750	91,431
Net income (loss)										115,800	153,497
Net (income) loss attributable to noncontrolling interest in consolidated joint ventures										138	(1,568)
Net (income) loss attributable to noncontrolling interest in operating partnership										(47,996)	(74,079)
Class A common stock
Real Estate [Line Items]
Net income attributable to Class A common shareholders	$ 36,106	$ 23,587	$ 22,113	$ 13,470	$ 41,856	$ 27,608	$ 2,802	$ (5,539)	$ 95,276	66,727	73,821
Class A common stock | Acquisitions
Real Estate [Line Items]
Net income attributable to Class A common shareholders										1,215	4,029
Class A common stock | Consolidated Pro Forma
Real Estate [Line Items]
Net income attributable to Class A common shareholders										$ 67,942	$ 77,850