SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Non-cash financing and investing activities:
Additions to property, plant and equipment acquired through finance obligations	$ 1,208	$ 623
Retirements of financed property, plant and equipment and related obligations	2,246
Purchase of property, plant and equipment in accounts payable at period end	$ 545	$ 1,337