Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	May 31, 2012	May 31, 2011	May 31, 2010
Income Tax Contingency [Line Items]
Income tax payments	$ 400,000	$ 400,000	$ 400,000
Received income tax refunds	100,000	13,100,000	16,800,000
Alternative Minimum Tax Credit Carryforward	28,808,000	28,808,000
Valuation allowance	5,200,000
Significant reserves for uncertain tax positions including related interest and penalties	0
Tax Credit Carryforwards, Alternative Minimum Tax
Income Tax Contingency [Line Items]
Alternative Minimum Tax Credit Carryforward	28,800,000
Federal
Income Tax Contingency [Line Items]
Federal Net operating Loss Carryforward	57,600,000
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Tax Benefit from Operating losses carryforwarded	$ 4,000,000
Operating Loss Carryforward Period	5
Operating Loss Carryforward Period	20