DEBT Schedules of convertible debt (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Debt Instrument [Line Items]
Debt component - net carrying value	$ 1,474,539	$ 1,474,539		$ 1,513,999
Amortization of debt discount		3,101	$ 101
Convertible Debt \| 4½% Convertible Senior Notes due 2023
Debt Instrument [Line Items]
Equity component - net carrying value (1)	36,778	36,778		36,778
Face amount due at maturity	143,750	143,750		143,750
Unamortized discount	(33,648)	(33,648)		(36,353)
Debt component - net carrying value	$ 110,102	$ 110,102		$ 107,397
Debt Instrument, Interest Rate, Effective Percentage	11.00%	11.00%
Contractual coupon interest	$ 1,636	$ 3,247
Amortization of debt discount	1,392	2,705
Total interest expense	3,028	5,952
Convertible Debt \| 4½% Convertible Senior Notes due 2023 \| Debt Issuance Cost [Member]
Debt Instrument [Line Items]
Equity component - net carrying value (1)	$ 1,000	$ 1,000

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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