EQUITY - Changes in common stock (Details) - shares	9 Months Ended
	Sep. 30, 2018	Sep. 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	583,738	366,679
Common Unit redemptions	25,839	52,808
Common stock issued for director fees	3,543	3,553
Forfeitures	(818)	(1,237)
Shares retained for employee tax withholding requirements	(187,850)	(59,111)
Ending common shares outstanding	104,745,710	104,266,587
Directors
Changes in Common Stock [Roll Forward]
Grants under the Equity Plan	34,130	28,426