Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE LOSS
Beginning Balance, Shares at Apr. 30, 2018		17,503,922
Beginning Balance at Apr. 30, 2018	$ 581,665	$ 361,158	$ 269,576	$ (49,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,767		24,767
Other comprehensive loss, net of tax	307			307
Stock-based compensation	786	$ 786
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares		43,048
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(1,241)	$ (1,241)
Employee benefit plan contributions, shares		41,408
Employee benefit plan contributions	3,623	$ 3,623
Ending Balance, Shares at Jul. 31, 2018		17,588,378
Ending Balance at Jul. 31, 2018	$ 609,907	$ 364,326	294,343	(48,762)
Beginning Balance, Shares at Apr. 30, 2019	16,849,026	16,849,026
Beginning Balance at Apr. 30, 2019	$ 620,353	$ 352,424	317,420	(49,491)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	26,881		26,881
Other comprehensive loss, net of tax	315			315
Stock-based compensation	897	$ 897
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares		20,923
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(1,050)	$ (1,050)
Employee benefit plan contributions, shares		45,721
Employee benefit plan contributions	$ 3,772	$ 3,772
Ending Balance, Shares at Jul. 31, 2019	16,915,670	16,915,670
Ending Balance at Jul. 31, 2019	$ 651,168	$ 356,043	$ 344,301	$ (49,176)