Income Taxes (Details Textual) - USD ($)	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015	May 31, 2014
Income Taxes (Textual) [Abstract]
Income tax expense (benefit)	$ 4,839,000	$ 40,337,000	$ (4,743,000)	$ (9,200,000)
Valuation allowance		(40,400,000)
Potential increase in equity if excess tax benefits are realized	600,000
Accrued interest and penalties	0	$ 0		$ 0
Unrecognized tax benefits	100,000
Additional unrecognized tax benefit	800,000
Foreign subsidiary undistributed earnings	5,300,000
Federal
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards after considering limitations of use	161,600,000
Tax Year 2017 To 2016 | Federal
Income Taxes (Textual) [Abstract]
Federal and State net operating loss carryforwards	29,800,000
Tax Year 2027 To 2033 | Federal
Income Taxes (Textual) [Abstract]
Net operating loss carryforwards after considering limitations of use	131,800,000
Tax Year 2015 To 2033 | State
Income Taxes (Textual) [Abstract]
Federal and State net operating loss carryforwards	$ 32,700,000