Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Deferred tax assets:
Accrued employee benefit expenses	$ 418	$ 549
Allowance for doubtful accounts	41	67
Deferred compensation	1,205	1,792
Tax credits	221	208
Unrecognized actuarial loss, defined benefit plans	1,825	3,223
Inventory Reserves	378	360
Net operating loss carryforwards	261	224
Other	79	113
Total deferred tax assets	4,428	6,536
Deferred tax liabilities:
Book basis in excess of tax basis of property, plant and equipment	(1,043)	(1,600)
Prepaid pension	(1,093)	(1,696)
Total deferred tax liabilities	(2,136)	(3,296)
Less: valuation allowance	(261)	(82)
Net deferred tax assets	2,031	3,158
Deferred tax assets classified in the balance sheet:
Non-current	2,031	3,158
Net deferred tax assets	$ 2,031	$ 3,158