Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock Sales of stock, private placement	Common Stock Initial public offering	Common Stock	Additional Paid-in Capital Sales of stock, private placement	Additional Paid-in Capital Initial public offering	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Sales of stock, private placement	Initial public offering	Total
Balance at Apr. 30, 2014			$ 324			$ 318,063	$ (18,953)					$ 299,434
Balance (in shares) at Apr. 30, 2014			32,341,752
Increase (Decrease) in Stockholders' Equity
Net income (loss)							(11,697)					(11,697)
Increase (decrease) in fair value of financial instruments, net of tax								$ 10				10
Equity-based compensation						6,455						6,455
Sales of common stock/Issuance of common stock in initial public offering, net of underwriting discounts and offering costs	$ 4			$ 5,366						$ 5,370
Sales of common stock/Issuance of common stock in initial public offering (in shares)	416,153
Balance at Apr. 30, 2015			$ 328			329,884	(30,650)	10				299,572
Balance (in shares) at Apr. 30, 2015			32,757,905
Increase (Decrease) in Stockholders' Equity
Net income (loss)							12,564					12,564
Change in accounting | Change in accounting for liability equity-based awards							(3,208)					(3,208)
Increase (decrease) in fair value of financial instruments, net of tax								(1,158)				(1,158)
Equity-based compensation						2,699						2,699
Stock repurchases									$ (5,827)			(5,827)
Stock repurchases (in shares)									394,577
Exercise of stock options			$ 1			1,661	(971)		$ 5,827			6,518
Exercise of stock options (in shares)			135,000						(394,577)
Balance at Apr. 30, 2016			$ 329			334,244	(22,265)	(1,148)				$ 311,160
Balance (in shares) at Apr. 30, 2016			32,892,905									32,892,905
Increase (Decrease) in Stockholders' Equity
Net income (loss)							48,886					$ 48,886
Increase (decrease) in fair value of financial instruments, 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			40,970,905									40,970,905