REVENUE RECOGNITION - Revenue Disaggregated by Product or Service (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	$ 394,876	$ 447,339	$ 685,864	$ 724,332
North America
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	53,863	59,331	103,915	124,618
Other Regions
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	341,013	$ 388,008	581,949	$ 599,714
Product revenue | North America
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	45,988		92,445
Product revenue | Other Regions
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	323,490		550,396
Processing and other revenues | North America
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	7,875		11,470
Processing and other revenues | Other Regions
Disaggregation of Revenue [Line Items]
Total sales and other operating revenues	$ 17,523		$ 31,553