Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Deferred tax assets:
Accrued employee benefit expenses	$ 549	$ 529
Allowance for doubtful accounts	67	74
Deferred compensation	1,792	1,753
Tax credits	208	224
Unrecognized actuarial loss, defined benefit plans	3,223	3,850
Inventory Reserves	360	118
Net operating loss carryforwards	224
Other	113	353
Total deferred tax assets	6,536	6,901
Deferred tax liabilities:
Book basis in excess of tax basis of property, plant and equipment	(1,600)	(1,655)
Prepaid pension	(1,696)	(1,854)
Total deferred tax liabilities	(3,296)	(3,509)
Less: valuation allowance	(82)
Net deferred tax assets	3,158	3,392
Deferred tax assets classified in the balance sheet:
Non-current	3,158	3,392
Net deferred tax assets	$ 3,158	$ 3,392