Other Financial Instruments and Fair Value Measurements (Details Textual) $ in Millions	6 Months Ended
	Oct. 31, 2018 USD ($)
Other Financial Instruments and Fair Value Measurements (Textual) [Abstract]
Company's Municipal bond mature in 2019	$ 1.4
Company's Municipal bond mature in 2020	0.9
Company's Municipal bond mature in 2021	1.0
Company's Municipal bond mature in 2022	1.0
Company's Municipal bond mature in 2023 and beyond	$ 31.5
Money market funds maturity period	three months or less