Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance, Shares at Apr. 30, 2018		17,503,922
Beginning Balance at Apr. 30, 2018	$ 581,665	$ 361,158	$ 269,576	$ (49,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	83,688		83,688
Other comprehensive income (loss), net of tax	(422)			(422)
Stock-based compensation	$ 3,040	$ 3,040
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	12,801	48,928
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ (1,241)	$ (1,241)
Stock repurchases, shares		(745,232)
Stock repurchases	(50,000)	$ (14,156)	(35,844)
Employee benefit plan contributions, shares		41,408
Employee benefit plan contributions	3,623	$ 3,623
Ending Balance, Shares at Apr. 30, 2019		16,849,026
Ending Balance at Apr. 30, 2019	620,353	$ 352,424	317,420	(49,491)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,861		74,861
Other comprehensive income (loss), net of tax	(1,682)			(1,682)
Stock-based compensation	$ 3,989	$ 3,989
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	5,167	31,790
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ (755)	$ (755)
Employee benefit plan contributions, shares		45,721
Employee benefit plan contributions	$ 3,772	$ 3,772
Ending Balance, Shares at Apr. 30, 2020	16,926,537	16,926,537
Ending Balance at Apr. 30, 2020	$ 700,538	$ 359,430	392,281	(51,173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58,763		58,763
Other comprehensive income (loss), net of tax	(3,395)			(3,395)
Stock-based compensation	$ 4,598	$ 4,598
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	0	29,019
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ (1,351)	$ (1,351)
Stock repurchases, shares		(200,046)
Stock repurchases	(20,000)	$ (3,896)	(16,104)
Employee benefit plan contributions, shares		45,591
Employee benefit plan contributions	$ 3,743	$ 3,743
Ending Balance, Shares at Apr. 30, 2021	16,801,101	16,801,101
Ending Balance at Apr. 30, 2021	$ 742,896	$ 362,524	$ 434,940	$ (54,568)