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Common Equity and Earnings Per Share - Additional Information (Detail) (USD $)
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9 Months Ended | 12 Months Ended |
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Sep. 30, 2012
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Dec. 31, 2011
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| Class of Stock | ||
| Payments of dividends, common stock | ||
| Preferred stock, shares issued | ||
| Preferred Stock, Shares Outstanding | ||
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Class A
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| Class of Stock | ||
| Common stock, votes per share | One | |
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Class B
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| Class of Stock | ||
| Common stock, votes per share | Ten |
| X | ||||||||||
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- Details
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| X | ||||||||||
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- Definition
Description of voting rights of common stock. Includes eligibility to vote and votes per share owned. Include also, if any, unusual voting rights. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Cash outflow in the form of ordinary dividends to common shareholders, generally out of earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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