Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Apr. 30, 2014	Apr. 30, 2013
Deferred tax assets:
Accrued employee benefit expenses	$ 462	$ 568
Allowance for doubtful accounts	68	52
Deferred compensation	1,432	1,688
Tax credits	304	336
Unrecognized actuarial loss, defined benefit plans	3,486	4,309
Other	98	86
Total deferred tax assets	5,850	7,039
Deferred tax liabilities:
Book basis in excess of tax basis of property, plant and equipment	(1,826)	(1,953)
Prepaid pension	(2,098)	(2,260)
Other	155	128
Total deferred tax liabilities	(3,769)	(4,085)
Less: valuation allowance	(50)	(59)
Net deferred tax assets (liabilities)	2,031	2,895
Deferred tax assets classified in the balance sheet:
Current	646	654
Non-current	1,385	2,241
Net deferred tax assets (liabilities)	$ 2,031	$ 2,895