Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Apr. 30, 2012
Deferred tax assets:
Accrued employee benefit expenses	$ 568	$ 480
Allowance for doubtful accounts	52	95
Deferred compensation	1,688	1,446
Tax credits	336	375
Unrecognized actuarial loss, defined benefit plans	4,309	4,146
Other	86	93
Total deferred tax assets	7,039	6,635
Deferred tax liabilities:
Book basis in excess of tax basis of property, plant and equipment	(1,953)	(2,166)
Prepaid pension	(2,260)	(2,180)
Other	128	153
Total deferred tax liabilities	(4,085)	(4,193)
Less: valuation allowance	(59)	(73)
Net deferred tax assets (liabilities)	2,895	2,369
Deferred tax assets classified in the balance sheet:
Current	654	713
Long-term	$ 2,241	$ 1,656