Stock-based Payments - Stock Option Activity (Details) - USD ($)		12 Months Ended
	Jul. 21, 2016	Apr. 30, 2018	Apr. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance		2,308,704	2,212,757
Shares, Granted	1,568,191	455,310	2,420,681
Shares, Exercised		(12,500)	0
Shares, Canceled		0	(1,793,779)
Shares, Forfeited		(7,042)	(421,487)
Shares, Expired		(38,627)	(109,468)
Shares, Outstanding, Ending Balance		2,705,845	2,308,704
Shares, Vested and expected to vest		2,705,845	2,308,704
Weighted Average Exercise Price, Vested and Expected to Vest (in usd per share)		$ 2.85
Shares, Vested		2,462,099	2,061,805
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding, Beginning Balance (in usd per share)		$ 2.86	$ 5.58
Weighted Average Exercise Price, Granted (in usd per share)	$ 2.10	3.01	1.99
Weighted Average Exercise Price, Exercised (in usd per share)		3.00	0.00
Weighted Average Exercise Price, Canceled (in usd per share)		0.00	4.92
Weighted Average Exercise Price, Forfeited (in usd per share)		6.86	2.03
Weighted Average Exercise Price, Expired (in usd per share)		5.21	7.86
Weighted Average Exercise Price, Outstanding, Ending Balance (in usd per share)		$ 2.85	2.86
Weighted Average Remaining Contractual Life, Granted		9 years 7 months 6 days
Aggregate Intrinsic Value, Granted		$ 603,000
Weighted Average Exercise Price, Vested (in usd per share)		$ 2.79	$ 2.93
Weighted Average Remaining Contractual Term, Outstanding, Beginning Balance (in years)		6 years 1 month 6 days	6 years 1 month 6 days
Weighted Average Remaining Contractual Term, Outstanding, Ending Balance (in years)		5 years 10 months 25 days	6 years 1 month 6 days
Weighted Average Remaining Contractual Life (Years), Vested and expected to vest		5 years 10 months 25 days	6 years 1 month 6 days
Weighted Average Remaining Contractual Life (Years), Vested		5 years 7 months 6 days	5 years 10 months 25 days
Aggregate Intrinsic Value, Outstanding, Beginning Balance		$ 1,282,000	$ 10,000
Aggregate Intrinsic Value, Outstanding, Ending Balance		5,265,000	1,282,000
Aggregate Intrinsic Value, Vested and expected to vest		5,265,000	1,282,000
Aggregate Intrinsic Value, Vested		$ 5,036,000	$ 1,101,000
Non- Employees
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance		50,000	51,250
Shares, Granted		0	0
Shares, Exercised		0	0
Shares, Canceled		0	0
Shares, Forfeited		0	0
Shares, Expired		0	(1,250)
Shares, Outstanding, Ending Balance		50,000	50,000
Shares, Vested and expected to vest		50,000	50,000
Shares, Vested		25,836	33,336
Directors and Employees
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance		2,258,704	2,161,507
Shares, Granted		455,310	2,420,681
Shares, Exercised		(12,500)	0
Shares, Canceled		0	(1,793,779)
Shares, Forfeited		(7,042)	(421,487)
Shares, Expired		(38,627)	(108,218)
Shares, Outstanding, Ending Balance		2,655,845	2,258,704
Shares, Vested and expected to vest		2,655,845	2,258,704
Shares, Vested		2,436,263	2,028,469