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, 2014		15,476,298
Beginning Balance at Apr. 30, 2014	$ 190,545	$ 127,371	$ 89,154	$ (25,980)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,499		35,499
Other comprehensive loss, net of tax	(14,877)			(14,877)
Stock-based compensation	3,497	3,497
Adjustments to excess tax benefit from stock-based compensation	$ 1,172	$ 1,172
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	508,639	599,124
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ 12,842	$ 12,842
Stock repurchases, shares		(163,326)
Stock repurchases	(5,053)	$ (1,098)	(3,955)
Employee benefit plan contributions, shares		167,575
Employee benefit plan contributions	6,217	$ 6,217
Ending Balance, Shares at Apr. 30, 2015		16,079,671
Ending 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	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)