Condensed Consolidated Statements Of Operations And Comprehensive Income (Loss) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012	Jan. 31, 2011
Condensed Consolidated Statements Of Operations And Comprehensive Income (Loss) [Abstract]
Tax effect of unrealized holding gains (losses) arising during the year	$ (199)	$ (122)	$ 1,113	$ (75)
Tax effect of reclassification adjustment for gains included in income		$ (602)	$ 58	$ (176)