EQUITY STRUCTURE AND ACCOUNTS - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	$ 1,648,074		$ 1,512,462	$ 1,643,635	[1]	$ 1,488,146
Other comprehensive income (loss)	(2,009)		1,445	16,775		(9,658)
Exchange of noncontrolling interest for common stock				0		0
Rebalancing of ownership percentage between Company and Operating Partnership				0		0
Ending Balance	1,639,250	[1]	1,553,643	1,639,250	[1]	1,553,643
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	12,171		(9,855)	(4,649)		(212)
Other comprehensive income (loss)	(1,804)		1,276	14,935		(8,230)
Exchange of noncontrolling interest for common stock				64		(167)
Rebalancing of ownership percentage between Company and Operating Partnership				17		27
Ending Balance	10,367		(8,582)	10,367		(8,582)
Accumulated Other Comprehensive Income (Loss) of Noncontrolling Interests
AOCI Attributable to Parent [Roll Forward]
Beginning Balance				(588)		116
Other comprehensive income (loss)				1,840		(1,428)
Exchange of noncontrolling interest for common stock				(64)		167
Rebalancing of ownership percentage between Company and Operating Partnership				(17)		(27)
Ending Balance	1,171		(1,172)	1,171		(1,172)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Beginning Balance				(5,237)		(96)
Ending Balance	$ 11,538		$ (9,754)	$ 11,538		$ (9,754)

[1] Includes amounts relating to consolidated variable interest entities. See Note 10.