INCOME TAXES (Tax rate) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
INCOME TAXES
Statutory federal tax rate (as a percent)			35.00%
State tax, low end of range of rate (as a percent)			6.00%
State tax, high end of range of rate (as a percent)			6.50%
Effective tax (benefit) rate (as a percent)	34.60%	37.50%	27.10%	37.80%
Alternative fuel tax credit (as a percent)		1.90%		8.60%