10. STOCKHOLDERS' EQUITY, COMPREHENSIVE INCOME AND STOCK-BASED COMPENSATION (Details 4) - shares	12 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2017
RSUs granted (in thousands)	0	(64)	(74)
Stock Option and RSU Transactions
Available Shares, Beginning (in thousands)	1,812	2,169	1,847
Additional shares reserved (in thousands)			2,238
Options granted (in thousands)	(804)	(338)	(368)
RSUs granted (in thousands)		(64)	(157)
RSUs cancelled (in thousands)	8	33
Options terminated (in thousands)	195	16	55
Plan shares expired (in thousands)	(64)	(4)	(1,446)
Available Shares, Ending (in thousands)	1,147	1,812	2,169