Consolidated Statements of Equity - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021
Common Stock [Member]
Statement [Line Items]
Balance (in shares)	13,642,185	13,591,889	13,478,733
Balance	$ 136	$ 136	$ 135
Issuance of common stock (in shares)	33,867	9,721	2,921
Issuance of common stock	$ 0	$ 0	$ 0
Stock options exercised (in shares)	25,416	40,575	110,235
Stock options exercised	$ 1		$ 1
Purchase of treasury shares	0	0	0
Stock based compensation	0	0	0
Dividends on subsidiary preferred stock	0	0	0
Net income	$ 0	$ 0	$ 0
Balance (in shares)	13,701,468	13,642,185	13,591,889
Balance	$ 137	$ 136	$ 136
Additional Paid-in Capital [Member]
Statement [Line Items]
Balance	103,113	98,812	88,559
Issuance of common stock	286	293	258
Stock options exercised	1,216	(1,488)	4,033
Purchase of treasury shares	0	0	0
Stock based compensation	5,314	5,496	5,962
Dividends on subsidiary preferred stock	0	0	0
Net income	0	0	0
Balance	109,929	103,113	98,812
Retained Earnings [Member]
Statement [Line Items]
Balance	665,410	570,436	465,656
Issuance of common stock	0	0	0
Stock options exercised	0	0	0
Purchase of treasury shares	0	0	0
Stock based compensation	0	0	0
Dividends on subsidiary preferred stock	(40)	(40)	(40)
Net income	20,432	95,014	104,820
Balance	685,802	665,410	570,436
Treasury Stock, Common [Member]
Statement [Line Items]
Balance	(292,225)	(257,527)	(246,911)
Issuance of common stock	0	0	0
Stock options exercised	0	0	0
Purchase of treasury shares	(5,196)	(34,698)	(10,616)
Stock based compensation	0	0	0
Dividends on subsidiary preferred stock	0	0	0
Net income	0	0	0
Balance	(297,421)	(292,225)	(257,527)
Noncontrolling Interest [Member]
Statement [Line Items]
Balance	100	100	100
Issuance of common stock	0	0	0
Stock options exercised	0	0	0
Purchase of treasury shares	0	0	0
Stock based compensation	0	0	0
Dividends on subsidiary preferred stock	0	0	0
Net income	0	0	0
Balance	100	100	100
Balance	476,534	411,957	307,539
Issuance of common stock	$ 286	$ 293	$ 258
Stock options exercised (in shares)	28,000	94,000	131,350
Stock options exercised	$ 1,217	$ (1,488)	$ 4,034
Purchase of treasury shares	(5,196)	(34,698)	(10,616)
Stock based compensation	5,314	5,496	5,962
Dividends on subsidiary preferred stock	(40)	(40)	(40)
Net income	20,432	95,014	104,820
Balance	$ 498,547	$ 476,534	$ 411,957