Income Taxes - Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	May 31, 2016	May 31, 2015
Current deferred tax assets
Accrued marketing programs	$ 181	$ 144
Accrued warranty expense	1,901	1,800
Accrued workers' compensation	1,011	886
Accrued vacation	346	325
Other	305	522
Gross current deferred tax assets	3,744	3,677
Noncurrent deferred tax assets
Liability for certain post-retirement benefits	1,850	2,017
Accrued warranty expense	987	958
Federal net operating loss carryforward	32,380	33,120
Federal tax credit carryforward	1,787	1,501
State net operating loss carryforward	7,717	8,133
Depreciation	714	668
Other	(171)	(167)
Gross noncurrent deferred tax assets	45,264	46,230
Total gross deferred tax assets	49,008	49,907
Valuation allowance	(49,008)	(49,907)
Net deferred tax assets	$ 0	$ 0