Investments In Available-For-Sale Securities (Contractual Maturities Of AFS Debt Securities At Varying Dates Over The Next 30 Years) (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2012	Apr. 30, 2011
Investments In Available-For-Sale Securities [Abstract]
Contractual maturities of AFS debt securities Cost Basis, Less than one year	$ 2,001
Contractual maturities of AFS debt securities Cost Basis, Two to five years	4,204
Contractual maturities of AFS debt securities Cost Basis, Six to ten years	1,056
Contractual maturities of AFS debt securities Cost Basis, Beyond	303,519
Contractual maturities of AFS debt securities Cost Basis, Total	310,780
Contractual maturities of AFS debt securities Fair Value, Less than one year	2,004
Contractual maturities of AFS debt securities Fair Value, Two to five years	4,502
Contractual maturities of AFS debt securities Fair Value, Six to ten years	1,206
Contractual maturities of AFS debt securities Fair Value, Beyond	306,475
Contractual maturities of AFS debt securities Fair Value, Total	$ 314,187	$ 166,917

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This item represents debt securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after five years and through ten years from the balance sheet date and which are categorized neither as held-to-maturity nor trading securities.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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