Inventories (Details) (USD $)	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Inventories [Abstract]
Raw materials	$ 13,756,000	$ 11,823,000
Work-in-process	19,179,000	17,170,000
Finished goods	13,439,000	11,318,000
Total FIFO inventories	46,374,000	40,311,000
Reserve to adjust inventories to LIFO value	(14,851,000)	(10,973,000)
Total LIFO inventories	31,523,000	29,338,000
Liquidation of LIFO based inventories	$ 0	$ 0	$ 125,000