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, 2016		16,244,041
Beginning Balance at Apr. 30, 2016	$ 280,761	$ 163,290	$ 164,756	$ (47,285)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	71,199		71,199
Other comprehensive loss, net of tax	6,868			6,868
Stock-based compensation	$ 3,469	$ 3,469
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	71,715	122,772
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ 633	$ 633
Stock repurchases, shares		(178,118)
Stock repurchases	(13,407)	$ (1,483)	(11,924)
Employee benefit plan contributions, shares		44,080
Employee benefit plan contributions	2,926	$ 2,926
Ending Balance, Shares at Apr. 30, 2017		16,232,775
Ending Balance at Apr. 30, 2017	352,449	$ 168,835	224,031	(40,417)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU 2018-02 | Accounting Standards Update 2018-02 [Member]			8,740	(8,740)
Net income	63,141		63,141
Other comprehensive 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	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 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)