EQUITY STRUCTURE AND ACCOUNTS - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	$ 1,488,146	[1]	$ 1,509,554		$ 1,491,408
Other comprehensive income (loss)	(5,141)		(2,220)		8,519
Exchange of noncontrolling interest for common stock	0		0		0
Rebalancing of ownership percentage between Company and Operating Partnership	0		0		0
Ending Balance	1,643,635	[1]	1,488,146	[1]	1,509,554
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(212)		1,365		(3,556)
Other comprehensive income (loss)	(4,211)		(2,915)		3,420
Exchange of noncontrolling interest for common stock	(167)		1,696		1,202
Rebalancing of ownership percentage between Company and Operating Partnership	(59)		(358)		(299)
Ending Balance	(4,649)		(212)		1,365
Accumulated Other Comprehensive Income of Noncontrolling Interests
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	116		759		(2,839)
Other comprehensive income (loss)	(930)		695		5,099
Exchange of noncontrolling interest for common stock	167		(1,696)		1,202
Rebalancing of ownership percentage between Company and Operating Partnership	59		358		(299)
Ending Balance	(588)		116		759
Total Accumulated Other Comprehensive Income
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(96)		2,124		(6,395)
Ending Balance	$ (5,237)		$ (96)		$ 2,124

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