Consolidated Balance Sheets (Parenthetical) (USD $)	Apr. 30, 2011	Apr. 30, 2010
Shareholders' Equity
Serial preferred shares, no par value, in USD per share	$ 0	$ 0
Serial preferred shares, shares authorized	3,000,000	3,000,000
Serial preferred shares, shares outstanding	0	0
Common shares, no par value, in USD per share	$ 0	$ 0
Common shares, shares authorized	150,000,000	150,000,000
Common shares, shares outstanding	114,172,122	119,119,152
Treasury shares, shares outstanding	14,432,043	9,485,013

Issuance value per share of no-par value common stock; generally not indicative of the fair market value per share.

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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-Section 02
-Paragraph 30
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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of shares of common stock held by shareholders. May be all or portion of the number of common shares authorized. These shares represent the ownership interest of the common shareholders. Excludes common shares repurchased by the entity and held as Treasury shares. Shares outstanding equals shares issued minus shares held in treasury. Does not include common shares that have been repurchased.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
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Issuance value per share of no-par value, nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer); generally not indicative of the fair market value per share.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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