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Summary Of Stock Option Activity (Detail) (USD $)
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9 Months Ended |
|---|---|
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Sep. 30, 2012
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |
| Outstanding at January 1, Shares | 1,818,640 |
| Granted, Shares | 196,469 |
| Exercised, Shares | (166,752) |
| Expired, Shares | (5,093) |
| Outstanding at September 30, Shares | 1,843,264 |
| Exercisable at September 30, Shares | 1,156,570 |
| Outstanding at January 1, Weighted Average Exercise Price | $ 30.94 |
| Granted, Weighted Average Exercise Price | $ 37.33 |
| Exercised, Weighted Average Exercise Price | $ 18.09 |
| Expired, Weighted Average Exercise Price | $ 43.33 |
| Outstanding at September 30, Weighted Average Exercise Price | $ 32.75 |
| Exercisable at September 30, Weighted Average Exercise Price | $ 33.93 |