Consolidated Statements Of Operations And Comprehensive Income (Loss) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Consolidated Statements Of Operations And Comprehensive Income (Loss) [Abstract]
Tax effect of unrealized holding gains arising during the year	$ (405)	$ (199)	$ (122)	$ 1,113
Tax effect of reclassification adjustment for gains (losses) included in income			$ 71	$ 58