PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
PROPERTY AND EQUIPMENT
Total property and equipment	$ 498,102		$ 498,102		$ 473,861
Accumulated depreciation and amortization	(232,482)		(232,482)		(215,418)
Property and equipment, net	265,620		265,620		258,443
Depreciation and amortization of plant and equipment	9,129	$ 7,044	17,254	$ 13,649
Cell development costs
PROPERTY AND EQUIPMENT
Total property and equipment	147,059		147,059		146,155
Land and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	53,067		53,067		50,481
Buildings and improvements
PROPERTY AND EQUIPMENT
Total property and equipment	91,743		91,743		91,358
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	162,388		162,388		154,014
Construction in progress
PROPERTY AND EQUIPMENT
Total property and equipment	$ 26,546		$ 26,546		$ 14,554