Share-Based Payments - Summary of Warrant Activity (Details) - USD ($)	9 Months Ended	12 Months Ended
	Jan. 31, 2019	Apr. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Aggregate Intrinsic Value, Exercised	$ 668,195
Aggregate Intrinsic Value, Canceled	$ 628,128
Warrants
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of Shares, Beginning Balance	2,004,284
Number of Shares, Granted	0
Number of Shares, Exercised	(247,468)
Number of Shares, Canceled	(85,376)
Number of Shares, Expired	0
Number of Shares, Ending Balance	1,671,440	2,004,284
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Exercise Price, Beginning Balance (in usd per share)	$ 5.57
Weighted Average Exercise Price, Granted (in usd per share)	0
Weighted Average Exercise Price, Exercised (in usd per share)	5.16
Weighted Average Exercise Price, Canceled (in usd per share)	4.80
Weighted Average Exercise Price, Expired (in usd per share)	0
Weighted Average Exercise Price, Ending Balance (in usd per share)	$ 5.58	$ 5.57
Weighted Average Remaining Contractual Life (in years)	1 year 1 month 13 days	1 year 9 months 18 days
Aggregate Intrinsic Value, Beginning Balance	$ 0
Aggregate Intrinsic Value, Ending Balance	$ 12,044,000	$ 0