Investments - Carrying value and fair value of securities available-for-sale (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Jul. 31, 2013	Apr. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 7,518	$ 6,295
Gross Unrealized Gains	923	767
Gross Unrealized Losses	(538)	(380)
Fair Value	7,903	6,682
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	103	103
Gross Unrealized Gains	34	27
Gross Unrealized Losses	(17)	(16)
Fair Value	120	114
ETFs - equities
Schedule of Available-for-sale Securities [Line Items]
Cost	3,878	3,878
Gross Unrealized Gains	889	740
Gross Unrealized Losses	(6)
Fair Value	4,761	4,618
Inverse ETFs - equities
Schedule of Available-for-sale Securities [Line Items]
Cost	3,537	2,314
Gross Unrealized Gains
Gross Unrealized Losses	(515)	(364)
Fair Value	$ 3,022	$ 1,950