Income Taxes (Details 1) (USD $) In Thousands, unless otherwise specified	May 31, 2013	May 31, 2012
Current deferred tax assets
Accrued marketing programs	$ 55	$ 207
Accrued warranty expense	1,466	1,560
Accrued workers' compensation	638	843
Accrued vacation	319	345
Other	143	180
Gross current deferred tax assets	2,621	3,135
Noncurrent deferred tax assets
Liability for certain post-retirement benefits	2,252	2,286
Accrued warranty expense	876	807
Federal net operating loss carryforward	26,616	22,747
Federal tax credit carryforward	1,205	1,038
State net operating loss carryforward	7,380	6,775
Depreciation	735	755
Other	(43)	(90)
Gross noncurrent deferred tax assets	39,021	34,318
Total gross deferred tax assets	41,642	37,453
Valuation allowance	(41,642)	(37,453)
Net deferred tax assets