Note 10 - Share-based Employee Compensation - Summary of Stock Option Activity (Details) - Stock Options Services-Based [Member] shares in Thousands	9 Months Ended
	Feb. 28, 2017 $ / shares shares
Outstanding, Shares (in shares) | shares	2,066
Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 7.89
Granted, Shares (in shares) | shares	1,126
Granted, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 3.46
Cancellations and Forfeitures, Shares (in shares) | shares	(40)
Cancellations and Forfeitures, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 4.53
Expired, Shares (in shares) | shares	(1,403)
Expired, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.62
Outstanding, Shares (in shares) | shares	1,749
Outstanding, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 6.13
Outstanding, Weighted Average Remaining Contractual Term (Year)	3 years 233 days
Exercisable, Shares (in shares) | shares	910
Exercisable, Weighted Average Exercise Price (in dollars per share) | $ / shares	$ 8.62
Exercisable, Weighted Average Remaining Contractual Term (Year)	1 year 36 days