Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock Initial public offering	Common Stock	Additional Paid-in Capital Initial public offering	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Initial public offering	Total
Balance at Apr. 30, 2015		$ 328		$ 329,884	$ (30,650)	$ 10			$ 299,572
Balance (in shares) at Apr. 30, 2015		32,758,000
Increase (Decrease) in Stockholders' Equity
Net income					12,564				12,564
Change in accounting | Change in accounting for liability equity-based awards					(3,208)				(3,208)
Change in other comprehensive income, net of tax						(1,158)			(1,158)
Equity-based compensation				2,699					2,699
Stock repurchases							$ (5,827)		(5,827)
Stock repurchases (in shares)							395
Exercise of stock options		$ 1		1,661	(971)		$ 5,827		6,518
Exercise of stock options (in shares)		135,000					(395)
Balance at Apr. 30, 2016		$ 329		334,244	(22,265)	(1,148)			311,160
Balance (in shares) at Apr. 30, 2016		32,893,000
Increase (Decrease) in Stockholders' Equity
Net income					48,886				48,886
Change in other comprehensive income, net of tax						264			264
Equity-based compensation				2,370					2,370
Sales of common stock/Issuance of common stock in initial public offering, net of underwriting discounts and offering costs	$ 80		$ 151,332					$ 151,412
Sales of common stock/Issuance of common stock in initial public offering (in shares)	8,050,000
Exercise of stock options		$ 1		513					514
Exercise of stock options (in shares)		28,000
Balance at Apr. 30, 2017		$ 410		488,459	26,621	(884)			$ 514,606
Balance (in shares) at Apr. 30, 2017		40,971,000							40,971,000
Increase (Decrease) in Stockholders' Equity
Net income					62,971				$ 62,971
Change in other comprehensive income, net of tax						1,325			1,325
Equity-based compensation				1,513					1,513
Tax withholding related to net share settlements of stock options				(1,441)					(1,441)
Exercise of stock options		$ 1		476					477
Exercise of stock options (in shares)		98,000
Balance at Apr. 30, 2018		$ 411		$ 489,007	$ 89,592	$ 441			$ 579,451
Balance (in shares) at Apr. 30, 2018		41,069,000							41,069,000