Condensed Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Apr. 30, 2019	13,376,030
Balance at Apr. 30, 2019	$ 134	$ 81,605	$ 409,573	$ (230,902)	$ 100	$ 260,510
Issuance of common stock (in shares)	552
Issuance of common stock	$ 0	40	0	0	0	40
Stock options exercised (in shares)	15,815
Stock options exercised	$ 0	80	0	0	0	80
Stock based compensation	0	1,620	0	0	0	1,620
Dividends on subsidiary preferred stock	0	0	(10)	0	0	(10)
Net income	0	0	15,511	0	0	15,511
Purchase of treasury shares	$ 0	0	0	(4,715)	0	(4,715)
Balance (in shares) at Jul. 31, 2019	13,392,397
Balance at Jul. 31, 2019	$ 134	83,345	425,074	(235,617)	100	273,036
Balance (in shares) at Apr. 30, 2019	13,376,030
Balance at Apr. 30, 2019	$ 134	81,605	409,573	(230,902)	100	260,510
Net income						29,398
Balance (in shares) at Oct. 31, 2019	13,410,528
Balance at Oct. 31, 2019	$ 134	84,772	438,951	(245,598)	100	278,359
Balance (in shares) at Jul. 31, 2019	13,392,397
Balance at Jul. 31, 2019	$ 134	83,345	425,074	(235,617)	100	273,036
Issuance of common stock (in shares)	631
Issuance of common stock	$ 0	50	0	0	0	50
Stock options exercised (in shares)	17,500
Stock options exercised	$ 0	785	0	0	0	785
Stock based compensation	0	592	0	0	0	592
Dividends on subsidiary preferred stock	0	0	(10)	0	0	(10)
Net income	0	0	13,887	0	0	13,887
Purchase of treasury shares	$ 0	0	0	(9,981)	0	(9,981)
Balance (in shares) at Oct. 31, 2019	13,410,528
Balance at Oct. 31, 2019	$ 134	84,772	438,951	(245,598)	100	278,359
Balance (in shares) at Apr. 30, 2020	13,478,733
Balance at Apr. 30, 2020	$ 135	88,559	460,876	(246,911)	100	302,759
Issuance of common stock (in shares)	675
Issuance of common stock	$ 0	50	0	0	0	50
Stock options exercised (in shares)	22,000
Stock options exercised	$ 0	1,166	0	0	0	1,166
Stock based compensation	0	2,320	0	0	0	2,320
Dividends on subsidiary preferred stock	0	0	(10)	0	0	(10)
Net income	$ 0	0	19,564	0	0	19,564
Balance (in shares) at Jul. 31, 2020	13,501,408
Balance at Jul. 31, 2020	$ 135	92,095	480,430	(246,911)	100	325,849
Balance (in shares) at Apr. 30, 2020	13,478,733
Balance at Apr. 30, 2020	$ 135	88,559	460,876	(246,911)	100	302,759
Net income						40,760
Balance (in shares) at Oct. 31, 2020	13,530,432
Balance at Oct. 31, 2020	$ 135	94,771	501,616	(252,991)	100	343,631
Balance (in shares) at Jul. 31, 2020	13,501,408
Balance at Jul. 31, 2020	$ 135	92,095	480,430	(246,911)	100	325,849
Issuance of common stock (in shares)	958
Issuance of common stock	$ 0	69	0	0	0	69
Stock options exercised (in shares)	28,066
Stock options exercised	$ 0	1,212	0	0	0	1,212
Stock based compensation	0	1,395	0	0	0	1,395
Dividends on subsidiary preferred stock	0	0	(10)	0	0	(10)
Net income	0	0	21,196	0	0	21,196
Purchase of treasury shares	$ 0	0	0	(6,080)	0	(6,080)
Balance (in shares) at Oct. 31, 2020	13,530,432
Balance at Oct. 31, 2020	$ 135	$ 94,771	$ 501,616	$ (252,991)	$ 100	$ 343,631