Investments (Narrative) (Details) (USD $)	12 Months Ended
Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Investments
Proceeds from the sales of AFS securities	$ 0	$ 2,100,000	$ 8,300,000
Gross realized gains on sales of AFS securities		0	700,000
Gross realized losses on sales of AFS securities		0	1,300,000
Other-than-temporary impairments of AFS securities	1,900,000	1,600,000	1,500,000
Held-to-maturity investment	$ 3,300,000	$ 6,000,000

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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+ Details

- Definition

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References+ Details

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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+ Details