Condensed Consolidated Statements of Equity (Unaudited) - USD ($) shares in Thousands, $ 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, 2018	13,147,143
Balance at Apr. 30, 2018	$ 131	$ 72,641	$ 361,987	$ (204,325)	$ 100	$ 230,534
Issuance of common stock (in shares)	544
Issuance of common stock		29				29
Stock options exercised (in shares)	131,357
Stock options exercised	$ 2	2,711				2,713
Purchase of treasury shares				(7,377)		(7,377)
Stock based compensation		1,094				1,094
Dividends on subsidiary preferred stock			(10)			(10)
Net income			10,884			10,884
Balance (in shares) at Jul. 31, 2018	13,279,044
Balance at Jul. 31, 2018	$ 133	76,475	372,861	(211,702)	100	237,867
Balance (in shares) at Apr. 30, 2018	13,147,143
Balance at Apr. 30, 2018	$ 131	72,641	361,987	(204,325)	100	230,534
Net income						22,164
Balance (in shares) at Oct. 31, 2018	13,326,400
Balance at Oct. 31, 2018	$ 133	78,142	384,132	(218,197)	100	244,310
Balance (in shares) at Jul. 31, 2018	13,279,044
Balance at Jul. 31, 2018	$ 133	76,475	372,861	(211,702)	100	237,867
Issuance of common stock (in shares)	580
Issuance of common stock		38				38
Stock options exercised (in shares)	46,776
Stock options exercised		1,035				1,035
Purchase of treasury shares				(6,495)		(6,495)
Stock based compensation		594				594
Dividends on subsidiary preferred stock			(10)			(10)
Net income			11,281			11,281
Balance (in shares) at Oct. 31, 2018	13,326,400
Balance at Oct. 31, 2018	$ 133	78,142	384,132	(218,197)	100	244,310
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		40				40
Stock options exercised (in shares)	15,815
Stock options exercised		80				80
Purchase of treasury shares				(4,715)		(4,715)
Stock based compensation		1,620				1,620
Dividends on subsidiary preferred stock			(10)			(10)
Net income			15,511			15,511
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		50				50
Stock options exercised (in shares)	17,500
Stock options exercised		785				785
Purchase of treasury shares				(9,981)		(9,981)
Stock based compensation		592				592
Dividends on subsidiary preferred stock			(10)			(10)
Net income			13,887			13,887
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