Basis of Presentation - Narrative (Details) - USD ($)	3 Months Ended
	Jul. 31, 2021	Jul. 31, 2020	Apr. 30, 2021	Apr. 30, 2020
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Percentage of LIFO Inventory	43.00%		43.00%
Inventories	$ 181,794,000		$ 158,167,000
Deferred Tax Assets, Net of Valuation Allowance	1,557,000		1,118,000
Retained earnings	432,137,000		448,282,000	$ 403,193,000
Net Cash Provided by (Used in) Operating Activities	6,588,000	$ 40,000,000
Impairment charges related to goodwill	0	0
Other intangible assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impairment charges related to other intangible assets	$ 0	0
Maximum
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Intangible assets estimated useful lives	6 years
Revision of Prior Period, Change in Accounting Principle, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Inventories	$ 2,204,000		17,885,000
Deferred Tax Assets, Net of Valuation Allowance			4,500,000
Retained earnings	$ 1,629,000		$ 13,342,000	$ 10,912,000
Net Cash Provided by (Used in) Operating Activities		$ 1,600,000