Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE LOSS
Balance at beginning of period (shares) at Apr. 30, 2020		16,926,537
Balance at beginning of period at Apr. 30, 2020	$ 711,450	$ 359,430	$ 403,193	$ (51,173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,059		16,059
Other comprehensive loss, net of tax	327			327
Stock-based compensation	961	$ 961
Exercise of stock-based compensation awards, net of amounts withheld for taxes (shares)		16,212
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(534)	$ (534)
Employee benefit plan contributions (shares)		45,591
Employee benefit plan contributions	3,743	$ 3,743
Balance at end of period (shares) at Jul. 31, 2020		16,988,340
Balance at end of period at Jul. 31, 2020	732,006	$ 363,600	419,252	(50,846)
Balance at beginning of period (shares) at Apr. 30, 2020		16,926,537
Balance at beginning of period at Apr. 30, 2020	711,450	$ 359,430	403,193	(51,173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39,181
Balance at end of period (shares) at Oct. 31, 2020		16,993,260
Balance at end of period at Oct. 31, 2020	756,546	$ 364,689	442,374	(50,517)
Balance at beginning of period (shares) at Jul. 31, 2020		16,988,340
Balance at beginning of period at Jul. 31, 2020	732,006	$ 363,600	419,252	(50,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,122		23,122
Other comprehensive loss, net of tax	329			329
Stock-based compensation	1,266	$ 1,266
Exercise of stock-based compensation awards, net of amounts withheld for taxes (shares)		4,920
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(177)	$ (177)
Balance at end of period (shares) at Oct. 31, 2020		16,993,260
Balance at end of period at Oct. 31, 2020	$ 756,546	$ 364,689	442,374	(50,517)
Balance at beginning of period (shares) at Apr. 30, 2021	16,801,101	16,801,101
Balance at beginning of period at Apr. 30, 2021	$ 756,238	$ 362,524	448,282	(54,568)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,981		2,981
Other comprehensive loss, net of tax	(200)			(200)
Stock-based compensation	1,177	$ 1,177
Exercise of stock-based compensation awards, net of amounts withheld for taxes (shares)		20,243
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(1,033)	$ (1,033)
Stock Repurchased and Retired During Period, Value	(25,000)		(19,126)
Stock Repurchased and Retired During Period, Shares		(299,781)
Employee benefit plan contributions (shares)		39,491
Employee benefit plan contributions	2,938	$ 2,938
Stock repurchases		$ 5,874
Balance at end of period (shares) at Jul. 31, 2021		16,561,054
Balance at end of period at Jul. 31, 2021	$ 737,101	$ 359,732	432,137	(54,768)
Balance at beginning of period (shares) at Apr. 30, 2021	16,801,101	16,801,101
Balance at beginning of period at Apr. 30, 2021	$ 756,238	$ 362,524	448,282	(54,568)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 5,011
Balance at end of period (shares) at Oct. 31, 2021	16,569,585	16,569,585
Balance at end of period at Oct. 31, 2021	$ 743,139	$ 360,902	434,167	(51,930)
Balance at beginning of period (shares) at Jul. 31, 2021		16,561,054
Balance at beginning of period at Jul. 31, 2021	737,101	$ 359,732	432,137	(54,768)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,030		2,030
Other comprehensive loss, net of tax	2,838			2,838
Stock-based compensation	1,216	$ 1,216
Exercise of stock-based compensation awards, net of amounts withheld for taxes (shares)		8,531
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ (46)	$ (46)
Balance at end of period (shares) at Oct. 31, 2021	16,569,585	16,569,585
Balance at end of period at Oct. 31, 2021	$ 743,139	$ 360,902	$ 434,167	$ (51,930)