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, 2013		14,822,580
Beginning Balance at Apr. 30, 2013	$ 146,195	$ 107,165	$ 71,180	$ (32,150)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,461		20,461
Other comprehensive income (loss), net of tax	6,170			6,170
Stock-based compensation	3,295	3,295
Adjustments to excess tax benefit from stock-based compensation	$ 600	$ 600
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares	551,485	643,558
Exercise of stock-based compensation awards, net of amounts withheld for taxes	$ 13,122	$ 13,122
Stock repurchases, shares		(100,000)
Stock repurchases	(3,141)	$ (654)	(2,487)
Employee benefit plan contributions, shares		110,160
Employee benefit plan contributions	3,843	$ 3,843
Ending Balance, Shares at Apr. 30, 2014		15,476,298
Ending 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 income (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	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 income (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)