5. Marketable Securities (Details) - Fair Value and Unrealized Losses, Aggregated by Investment Type and Length of Time Individual Securities have been Continuious Unrealized Loss Position (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
5. Marketable Securities (Details) - Fair Value and Unrealized Losses, Aggregated by Investment Type and Length of Time Individual Securities have been Continuious Unrealized Loss Position [Line Items]
Fair Value, Less than 12 months		$ 840
Unrealized Losses, Less than 12 months		(175)
Fair Value, More than 12 months	512	0
Unrealized Losses, More than 12 months	(68)	0
Fair Value	512	840
Unrealized Losses	(68)	(175)
Fixed Income Securities [Member]
5. Marketable Securities (Details) - Fair Value and Unrealized Losses, Aggregated by Investment Type and Length of Time Individual Securities have been Continuious Unrealized Loss Position [Line Items]
Fair Value, Less than 12 months	0	301
Unrealized Losses, Less than 12 months	0	(6)
Fair Value, More than 12 months	0	0
Unrealized Losses, More than 12 months	0	0
Fair Value	0	301
Unrealized Losses	0	(6)
Equity Securities [Member]
5. Marketable Securities (Details) - Fair Value and Unrealized Losses, Aggregated by Investment Type and Length of Time Individual Securities have been Continuious Unrealized Loss Position [Line Items]
Fair Value, Less than 12 months	0	539
Unrealized Losses, Less than 12 months	0	(169)
Fair Value, More than 12 months	512	0
Unrealized Losses, More than 12 months	(68)	0
Fair Value	512	539
Unrealized Losses	$ (68)	$ (169)