EQUITY STRUCTURE AND ACCOUNTS - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	$ 1,644,243		$ 1,503,292	$ 1,643,635	[1]	$ 1,488,146
Other comprehensive income (loss)	5,589		(2,247)	18,782		(11,104)
Exchange of noncontrolling interest for common stock				0		0
Rebalancing of ownership percentage between Company and Operating Partnership				0		0
Ending Balance	1,648,074	[1]	1,512,462	1,648,074	[1]	1,512,462
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	7,080		(7,880)	(4,649)		(212)
Other comprehensive income (loss)	5,007		(1,978)	16,738		(9,506)
Exchange of noncontrolling interest for common stock				65		(143)
Rebalancing of ownership percentage between Company and Operating Partnership				17		6
Ending Balance	12,171		(9,855)	12,171		(9,855)
Accumulated Other Comprehensive Income (Loss) of Noncontrolling Interests
AOCI Attributable to Parent [Roll Forward]
Beginning Balance				(588)		116
Other comprehensive income (loss)				2,044		(1,598)
Exchange of noncontrolling interest for common stock				(65)		143
Rebalancing of ownership percentage between Company and Operating Partnership				(17)		(6)
Ending Balance	1,374		(1,345)	1,374		(1,345)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Beginning Balance				(5,237)		(96)
Ending Balance	$ 13,545		$ (11,200)	$ 13,545		$ (11,200)

[1] Includes amounts relating to consolidated variable interest entities. See Note 3.