Investments (Schedule of Contractual Maturities of AFS Debt Securities) (Details) (USD $) In Thousands	Apr. 30, 2011
Investments
Cost basis, less than one year	$ 3,023
Cost basis, two to five years	3,112
Cost basis, six to ten years	2,200
Cost basis, beyond	157,970
Cost basis, total AFS securities	166,305
Fair value, less than one year	3,081
Fair value, two to five years	3,331
Fair value, six to ten years	2,328
Fair value, beyond	158,177
Fair Value, total AFS securities	$ 166,917