Stock-based Payments - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance	2,004,002	1,945,920
Shares, Granted	343,749	1,763,381
Shares, Exercised	0	(313)
Shares, Canceled	0	(1,656,073)
Shares, Forfeited	(42,515)	(12,604)
Shares, Expired	(92,479)	(36,309)
Shares, Outstanding, Ending Balance	2,212,757	2,004,002
Shares, Vested and expected to vest	2,212,757	2,004,002
Shares, Vested	1,737,306	1,425,923
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)	$ 5.74	$ 12.12
Grants in period, weighted average exercise price (in usd per share)	5.33	7.92
Weighted Average Exercise Price, Exercised (in usd per share)	0.00	5.88
Weighted Average Exercise Price, Canceled (in usd per share)	0.00	12.48
Weighted Average Exercise Price, Forfeited (in usd per share)	6.90	11.52
Weighted Average Exercise Price, Expired (in usd per share)	6.97	11.88
Weighted Average Exercise Price, Outstanding, Ending Balance (in usd per share)	5.58	5.74
Weighted Average Exercise Price, Vested (in usd per share)	$ 5.71	$ 5.88
Weighted Average Remaining Contractual Term, Outstanding, Beginning Balance (in years)	6 years 8 months 12 days	7 years 6 months
Weighted Average Remaining Contractual Term, Outstanding, Ending Balance (in years)	6 years 1 month 6 days	6 years 8 months 12 days
Weighted Average Remaining Contractual Life (Years), Vested and expected to vest	6 years 1 month 6 days	6 years 8 months 12 days
Weighted Average Remaining Contractual Life (Years), Vested	5 years 7 months 6 days	5 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 4,166	$ 985
Aggregate Intrinsic Value, Outstanding, Ending Balance	10	4,166
Aggregate Intrinsic Value, Vested and expected to vest	10	4,166
Aggregate Intrinsic Value, Vested	$ 9	$ 2,879
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance	57,917	63,750
Shares, Granted	0	6,667
Shares, Exercised	0	0
Shares, Canceled	0	0
Shares, Forfeited	0	0
Shares, Expired	(6,667)	(12,500)
Shares, Outstanding, Ending Balance	51,250	57,917
Shares, Vested and expected to vest	51,250	57,917
Shares, Vested	34,271	40,625
Directors and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance	1,946,085	1,882,170
Shares, Granted	343,749	1,756,714
Shares, Exercised	0	(313)
Shares, Canceled	0	(1,656,073)
Shares, Forfeited	(42,515)	(12,604)
Shares, Expired	(85,812)	(23,809)
Shares, Outstanding, Ending Balance	2,161,507	1,946,085
Shares, Vested and expected to vest	2,161,507	1,946,085
Shares, Vested	1,703,035	1,385,298