BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Mar. 31, 2017
Cash and Cash Equivalents [Line Items]
Value added tax expense	$ 5,958,000	$ 7,244,000	$ 9,834,000	$ 11,098,000
Cash and cash equivalents	116,970,000	188,936,000	116,970,000	188,936,000	$ 264,660,000	$ 473,110,000
Cash held on deposit	1,256,000	2,010,000	1,256,000	2,010,000	1,261,000
Cash restricted for capital investment	850,000	0	850,000	0	1,487,000
Purchases of property, plant and equipment		245,000	1,637,000
Sales of property, plant and equipment			1,430,000	82,000
Collections on beneficial interests on securitized trade receivables			114,212,000	118,118,000
Interest expense	35,324,000	33,099,000	68,235,000	67,540,000
Accounting Standards Update 2016-15
Cash and Cash Equivalents [Line Items]
Cash collections from beneficial interests	118,118,000		118,118,000
Collections on beneficial interests on securitized trade receivables			110,763,000
Accounting Standards Update 2016-18
Cash and Cash Equivalents [Line Items]
Restricted cash		2,661,000		2,661,000	$ 3,373,000
Change in restricted cash				352,000
Interest expense		$ 343,000		$ 684,000
Zimbabwe | Cash Held in Real Time Gross Settlement System
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 340,000		$ 340,000