EQUITY STRUCTURE AND ACCOUNTS - Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
AOCI Attributable to Parent [Roll Forward]
Balance at the beginning of the year			$ 1,365
Other comprehensive income (loss)	$ (2,225)	$ (8,576)	3,701	$ 53,275	$ 8,519
Exchange of noncontrolling interest for common stock			(2,083)		0
Balance at the end of the year	4,398		4,398		1,365
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent [Roll Forward]
Balance at the beginning of the year			1,365	(3,556)	(3,556)
Other comprehensive income (loss)			1,854	30,171	3,420
Exchange of noncontrolling interest for common stock			1,422	928	1,202
Rebalancing of ownership percentage between Company and Operating Partnership			(243)	350
Balance at the end of the year	4,398	27,893	4,398	27,893	1,365
Accumulated Other Comprehensive Income of Noncontrolling Interests
AOCI Attributable to Parent [Roll Forward]
Balance at the beginning of the year			761	(2,839)	(2,839)
Other comprehensive income (loss)			1,847	23,104
Exchange of noncontrolling interest for common stock			(1,422)	(928)
Rebalancing of ownership percentage between Company and Operating Partnership			243	(350)
Balance at the end of the year	1,429	18,987	1,429	18,987	761
Total Accumulated Other Comprehensive Income
AOCI Attributable to Parent [Roll Forward]
Balance at the beginning of the year			2,126	(6,395)	(6,395)
Other comprehensive income (loss)			3,701	53,275
Exchange of noncontrolling interest for common stock			0	0
Rebalancing of ownership percentage between Company and Operating Partnership			0	0
Balance at the end of the year	$ 5,827	$ 46,880	$ 5,827	$ 46,880	$ 2,126