DEBT - INTEREST EXPENSE COMPONENTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017		Jun. 18, 2013
Debt Instrument [Line Items]
Non-cash amortization of discount on Convertible Notes	$ 91	$ 15,662	[1]	$ 21,222	[1]
Amortization of debt issuance costs	$ 809	578	[1]	1,227	[1]
1.00% Convertible Notes due 2018
Debt Instrument [Line Items]
Interest rate	1.00%
Convertible Debt | 1.00% Convertible Notes due 2018
Debt Instrument [Line Items]
Interest rate						1.00%
Cash interest expense (coupon interest expense)	$ 1	539		2,784
Non-cash amortization of discount on Convertible Notes	91	15,662		14,221
Amortization of debt issuance costs	3	466		453
Total interest expense related to Convertible Notes	$ 95	$ 16,667		$ 17,458

[1] Prior period amounts have been adjusted retrospectively to reflect the adoption of ASU 2016-18, Statement of Cash Flows (Topic 230): RestrictedCash. Refer to Note 1 for further discussion.