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Treasury Stock - Additional Information (Detail) (USD $)
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9 Months Ended | |||
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Sep. 30, 2013
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Dec. 31, 2012
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Sep. 30, 2013
Two Thousand Five Share Repurchase Program
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Sep. 30, 2013
Two Thousand Five Share Repurchase Program
Class A
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| Equity, Class of Treasury Stock [Line Items] | ||||
| Stock authorized to repurchase by board of directors | $ 800,000,000 | |||
| Treasury stock, shares | 6,405,000 | 6,405,000 | 3,826,947 | |
| Shares repurchased, average price per share | $ 90.23 | |||
| Treasury stock, cost | $ 475,184,000 | $ 475,184,000 | $ 345,300,000 | |
| Shares repurchased program expiration date | Apr. 29, 2018 | |||