Restructuring Charges (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jul. 31, 2019	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Restructuring and Related Activities [Abstract]
Restructuring charges, net		$ 5,848,000	$ (18,000)	$ 1,987,000
Restructuring reserve		139,000	189,000	387,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		5,848,000	(18,000)	$ 1,987,000
Employee Severance and Separation [Member]
Restructuring and Related Activities [Abstract]
Restructuring charges, net		1,739,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		1,739,000
Nationwide Reductions In Force
Restructuring and Related Activities [Abstract]
Restructuring charges, net	$ 1,800,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net	$ 1,800,000
Manufacturing Plant Closure
Restructuring and Related Activities [Abstract]
Restructuring charges, net		4,400,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		4,400,000
Manufacturing Plant Closure | Employee Severance and Separation [Member]
Restructuring and Related Activities [Abstract]
Restructuring charges, net		900,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		900,000
Manufacturing Plant Closure | Other Restructuring
Restructuring and Related Activities [Abstract]
Restructuring charges, net		3,500,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		3,500,000
Nationwide Reductions In Force | Employee Severance and Separation [Member]
Restructuring and Related Activities [Abstract]
Restructuring charges, net		1,400,000	200,000
Restructuring Cost and Reserve [Line Items]
Restructuring charges, net		1,400,000	$ 200,000
Discontinued Operations, Disposed of by Sale | Humboldt Facility | Facility Closing
Restructuring and Related Activities [Abstract]
Gain (Loss) on Disposition of Business		2,300,000
Restructuring Cost and Reserve [Line Items]
Gain (Loss) on Disposition of Business		$ 2,300,000