INCOME TAXES - Reconciliation of Taxes Provided to Federal Statutory Rate (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2017	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Tax benefit at statutory rate		$ (36,163)	$ (18,441)	$ (11,790)
State income taxes before valuation allowance, net of federal effect		(7,680)	(3,612)	(1,042)
Foreign tax rate differential		(1,422)	71	(1,188)
Research and development credits		(3,892)	(3,744)	(2,189)
Change in valuation allowance		51,741	30,558	56,663
Compensation/option differences		(6,584)	(7,277)	(4,965)
Non-deductible compensation		3,017	1,200	1,132
Tax Act rate change impact	$ 23,000	0	0	22,630
Foreign loss not benefited		107	159	6,847
Other		1,708	1,655	196
Total income tax provision (benefit)		$ 832	$ 569	$ 66,294

Amount of current and deferred foreign income tax expense (benefit) attributable to income (loss) from continuing operations.

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