Organization, Use of Estimates and Basis of Presentation - Calculation of Earnings Per Share (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Basic loss per share computation
Net loss attributable to common stockholders	$ (1,408,904)	$ (2,412,381)	$ (4,459,773)	$ (7,872,115)
Weighted average common shares outstanding, basic (in shares)	10,967,738	8,702,237	10,130,460	8,702,237
Basic and diluted net loss per share (in dollars per share)	$ (0.13)	$ (0.28)	$ (0.44)	$ (0.90)