Investments - Composition of income from securities transactions (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Jan. 31, 2013		Jan. 31, 2012		Jan. 31, 2013		Jan. 31, 2012
Investment Income, Net [Abstract]
Dividend income	$ 34		$ 19		$ 91		$ 46
Interest income	3		2		4		16
Realized losses on securities available-for-sale (1)		[1]	(18)	[1]		[1]	(22)	[1]
Other					(2)		(6)
Total income from securities transactions, net	$ 37		$ 3		$ 93		$ 34

[1] This amount was reclassified from Accumulated Other Comprehensive Income in the Consolidated Condensed Balance Sheets to the Consolidated Condensed Statements of Income.