PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
PROPERTY AND EQUIPMENT
Total property and equipment	$ 419,498		$ 419,498		$ 393,145
Accumulated depreciation and amortization	(188,624)		(188,624)		(166,908)
Property and equipment, net	230,874		230,874		226,237
Depreciation and amortization of plant and equipment	7,386	$ 6,454	21,007	$ 18,561
Cell development costs
PROPERTY AND EQUIPMENT
Total property and equipment	141,522		141,522		128,821
Land and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	36,302		36,302		34,285
Buildings and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	85,774		85,774		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	117,066		117,066		110,267
Construction in progress
PROPERTY AND EQUIPMENT
Total property and equipment	$ 21,535		$ 21,535		$ 24,392