Inventories - Additional Information (Detail) (USD $)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Inventories Net [Line Items]
LIFO inventory reserve	$ 1,300,000	$ 1,600,000
Increase or Decrease in cost of sales as a result of liquidation of LIFO inventory	(273,000)	146,000
International Subsidiaries [Member]
Inventories Net [Line Items]
Inventories measured using FIFO method	$ 2,077,000	$ 1,253,000
Maximum [Member]
Inventories Net [Line Items]
LIFO Index	100.00%	100.00%