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, 2015		16,079,671
Beginning Balance at Apr. 30, 2015	$ 229,842	$ 150,001	$ 120,698	$ (40,857)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	58,723		58,723
Other comprehensive loss, net of tax	(6,428)			(6,428)
Stock-based compensation	3,609	3,609
Adjustments to excess tax benefit from stock-based compensation	$ 4,559	$ 4,559
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	287,975	375,928
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ 5,288	$ 5,288
Stock repurchases, shares		(243,143)
Stock repurchases	(16,593)	$ (1,928)	(14,665)
Employee benefit plan contributions, shares		31,585
Employee benefit plan contributions	1,761	$ 1,761
Ending Balance, Shares at Apr. 30, 2016		16,244,041
Ending 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	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)