EQUITY - Changes in common stock (Details) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Changes in Common Stock [Roll Forward]
Beginning common shares outstanding	93,525,469	86,793,521
Stock Offering	10,350,000	0
Common Unit redemptions	52,808	61,056
Common stock issued for director fees	3,553	5,851
Forfeitures	(1,237)	(406)
Shares retained for employee tax withholding requirements	(59,111)	(61,622)
Ending common shares outstanding	104,266,587	87,314,950
Directors
Changes in Common Stock [Roll Forward]
Grants under the equity compensation plans	28,426	32,180
Equity Plan
Changes in Common Stock [Roll Forward]
Grants under the equity compensation plans	366,679	446,686
Exercise of stock options	0	37,684