Investments - Composition of income from securities transactions (Details 1) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Dividend income	$ 31	$ 42	$ 111	$ 119
Interest income				3
Capital gain distributions	105	57	105	57
Realized capital loss			(15)
Other	(3)	(3)	14	24
Total income from securities transactions, net	$ 133	$ 96	$ 215	$ 203