Note 1 - Schedule of Fair Value Measurements of Investments (Details) - USD ($)	Jul. 31, 2016	Apr. 30, 2016
Fair Value, Inputs, Level 1 [Member]
Cash and Cash Equivalents, Fair Value Disclosure	$ 19,846,000	$ 12,037,000
Available-for-sale Securities	3,875,000	3,637,000
	23,721,000	15,674,000
Fair Value, Inputs, Level 2 [Member]
Cash and Cash Equivalents, Fair Value Disclosure
Available-for-sale Securities
Fair Value, Inputs, Level 3 [Member]
Cash and Cash Equivalents, Fair Value Disclosure
Available-for-sale Securities
Cash and Cash Equivalents, Fair Value Disclosure	19,846,000	12,037,000
Available-for-sale Securities	3,875,000	3,637,000
	$ 23,721,000	$ 15,674,000