PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
PROPERTY AND EQUIPMENT
Total property and equipment	$ 410,972		$ 410,972		$ 393,145
Accumulated depreciation and amortization	(180,855)		(180,855)		(166,908)
Property and equipment, net	230,117		230,117		226,237
Depreciation and amortization of plant and equipment	6,987	$ 6,202	13,621	$ 12,106
Cell development costs
PROPERTY AND EQUIPMENT
Total property and equipment	130,458		130,458		128,821
Land and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	34,557		34,557		34,285
Buildings and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	81,347		81,347		78,081
Railcars
PROPERTY AND EQUIPMENT
Total property and equipment	17,299		17,299		17,299
Vehicles and other equipment
PROPERTY AND EQUIPMENT
Total property and equipment	114,215		114,215		110,267
Construction in progress
PROPERTY AND EQUIPMENT
Total property and equipment	$ 33,096		$ 33,096		$ 24,392