EQUITY - Changes in common stock (Details) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Changes in Common Stock [Roll Forward]
Beginning common shares outstanding	104,287,128	93,525,469
Stock Offering	0	10,350,000
Grants under the Equity Plan	583,373	366,679
Common Unit redemptions	25,839	30,657
Common stock issued for director fees	2,299	2,454
Forfeitures	(818)	(1,237)
Shares retained for employee tax withholding requirements	(187,850)	(59,111)
Ending common shares outstanding	104,744,101	104,238,807
Directors
Changes in Common Stock [Roll Forward]
Grants under the Equity Plan	34,130	23,896