Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	COMMON STOCK	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE LOSS
Beginning Balance, Shares at Apr. 30, 2017		16,232,775
Beginning Balance at Apr. 30, 2017	$ 352,449	$ 168,835	$ 224,031	$ (40,417)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,036		22,281
Other comprehensive loss, net of tax	244			244
Stock-based compensation	945	$ 945
Exercise of stock-based compensation awards, net of amounts withheld for taxes, shares		79,071
Exercise of stock-based compensation awards, net of amounts withheld for taxes	(1,490)	$ (1,490)
Stock repurchases, shares		(56,700)
Stock repurchases	(5,562)	$ (479)	(5,083)
Employee benefit plan contributions, shares		36,264
Employee benefit plan contributions	3,554	$ 3,554
Ending Balance, Shares at Oct. 31, 2017		16,291,410
Ending Balance at Oct. 31, 2017	$ 372,421	$ 171,365	241,229	(40,173)
Beginning Balance, Shares at Apr. 30, 2018	17,503,922	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
Ending Balance at Jul. 31, 2018	$ 609,907
Beginning Balance, Shares at Apr. 30, 2018	17,503,922	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	43,255		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 Oct. 31, 2018	17,588,378	17,588,378
Ending Balance at Oct. 31, 2018	$ 616,339	$ 364,326	294,343	(48,762)
Beginning Balance at Jul. 31, 2018	609,907
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 18,488
Ending Balance, Shares at Oct. 31, 2018	17,588,378	17,588,378
Ending Balance at Oct. 31, 2018	$ 616,339	$ 364,326	$ 294,343	$ (48,762)