Common Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Jun. 15, 2016	Jul. 31, 2016	Jul. 31, 2015	Apr. 30, 2016
Class of Stock [Line Items]
Common stock, par value (in dollars per share)		$ 0.001		$ 0.001
Issuance of common stock	$ 4,300
Offering-related expense	$ 742	$ 0	$ 18
Common Stock [Member]
Class of Stock [Line Items]
Shares issued in offering (in shares)	2,000,000
Common stock, par value (in dollars per share)	$ 0.001
Share price (in usd per share)	$ 2.25
Over-Allotment Option [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares issued in offering (in shares)	258,749