EQUITY - Changes in common stock (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Beginning common shares outstanding	93,525,469	86,793,521
Common stock issued	10,350,000	6,151,514
Common Unit redemptions	73,322	119,308
Forfeitures	(2,320)	(1,420)
Shares retained for employee tax withholding requirements	(59,111)	(61,622)
Ending common shares outstanding	104,287,128	93,525,469
Equity Plan
Class of Stock [Line Items]
Grants under the Equity Plan	366,679	446,686
Exercise of stock options	0	37,684
Directors
Class of Stock [Line Items]
Grants under the Equity Plan	28,426	32,180
Common stock issued for director fees	4,663	7,618