Note 10 - Share-based Employee Compensation - Summary of Stock Option Activity (Details)	12 Months Ended
	May 31, 2016 $ / shares shares
Stock Options Services-Based [Member]
Outstanding (in shares) | shares	2,441,000
Outstanding (in dollars per share) | $ / shares	$ 7.78
Cancellations and forfeitures (in shares) | shares	(270,000)
Cancellations and forfeitures (in dollars per share) | $ / shares	$ 6.51
Expired (in shares) | shares	(105,000)
Expired (in dollars per share) | $ / shares	$ 8.83
Outstanding (in shares) | shares	2,066,000
Outstanding (in dollars per share) | $ / shares	$ 7.89
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	3 years 14 days
Exercisable at end of year (in shares) | shares	1,671,000
Exercisable at end of year (in dollars per share) | $ / shares	$ 8.20
Exercisable at end of year	2 years 219 days
Stock Options Performance-based [Member]
Outstanding (in shares) | shares	515,000
Outstanding (in dollars per share) | $ / shares	$ 8.60
Cancellations and forfeitures (in shares) | shares	(515,000)
Cancellations and forfeitures (in dollars per share) | $ / shares	$ 8.60
Outstanding (in shares) | shares	0
Outstanding (in dollars per share) | $ / shares	$ 0