Note 6 - Comprehensive Income - Components of Comprehensive Income That Are Included In Consolidated Statement of Changes in Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Change in unrealized gains (losses) on securities, amount before tax			$ 978	$ 271
Change in unrealized gains (losses) on securities, tax expense			(105)	(96)
Change in unrealized gains (losses) on securities, amount net of tax			873	175
Less: Gains realized in net income, amount before tax			(152)	(39)
Less: Gains realized in net income, tax expense			32	14
Less: Gains realized in net income, amount net of tax			(120)	(25)
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax			826	232
Other comprehensive income (loss), available-for-sale securities, tax expense			(73)	(82)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ 496	$ 290	$ 753	$ 150