EQUITY - Changes in common stock (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in Common Stock [Roll Forward]
Beginning common shares outstanding	104,287,128	93,525,469
Grants under the Equity Plan	583,373	316,142
Common Unit redemptions	0	10,657
Common stock issued for director fees	1,147	1,259
Shares retained for employee tax withholding requirements	(187,850)	(42,355)
Ending common shares outstanding	104,683,798	93,811,172