7. INCOME TAXES (Details 2)	12 Months Ended
May 31, 2018	May 31, 2017	May 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. federal statutory tax rate	28.60%	34.00%	34.00%
State taxes, net of federal tax effect	(16.70%)	(0.10%)	0.00%
Foreign rate differential	39.40%	0.10%	0.20%
Stock-based compensation	39.90%	(2.80%)	(3.80%)
Research and development credit	5.90%	3.10%	2.10%
Change in valuation allowance	(1349.20%)	(33.80%)	(32.50%)
Federal rate change impact	1419.70%	0.00%	0.00%
Federal AMT refund	(20.00%)	(0.00%)	(0.00%)
ASU 2016-09 adoption	(169.10%)	0.00%	0.00%
Other	5.40%	(0.90%)	(0.20%)
Effective tax rate	(16.10%)	(0.40%)	(0.20%)

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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