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, 2017		16,232,775
Beginning Balance at Apr. 30, 2017	$ 352,449	$ 168,835	$ 224,031	$ (40,417)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	63,141		63,141
Other comprehensive income (loss), net of tax	88			88
Stock-based compensation	$ 3,097	$ 3,097
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	36,950	86,927
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ (1,513)	$ (1,513)
Stock issuance related to acquisition, shares		1,457,568
Stock issuance related to acquisition	189,849	$ 189,849
Stock repurchases, shares		(309,612)
Stock repurchases	(29,000)	$ (2,664)	(26,336)
Employee benefit plan contributions, shares		36,264
Employee benefit plan contributions	3,554	$ 3,554
Ending Balance, Shares at Apr. 30, 2018		17,503,922
Ending 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	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)