Quarterly report pursuant to Section 13 or 15(d)

Summary Of Stock Option Activity (Detail)

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Summary Of Stock Option Activity (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Shares    
Beginning balance 1,073,800 881,000
Granted 41,500 166,500
Exercised 54,036 23,000
Ending balance 1,048,764 1,024,500
Exercisable end of period 443,589 418,974
Weighted Average Exercise Price    
Beginning balance $ 18.33 $ 15.65
Granted $ 30.00 $ 26.05
Exercised $ 11.07 $ 10.89
Ending balance $ 19.11 $ 17.34
Exercisable at end of period $ 13.40 $ 12.81
Weighted Average Remaining Contractual Term (years)    
Beginning balance 6 years 6 years 10 months 24 days
Granted 9 years 8 months 12 days 9 years 7 months 6 days
Exercised 3 years 7 months 6 days 4 years 4 months 24 days
Ending balance 5 years 9 months 18 days 6 years 2 months 12 days
Exercisable at end of period 3 years 10 months 24 days 4 years 9 months 18 days
Aggregate Intrinsic Value    
Beginning balance $ 12,508 $ 8,238
Exercised 1,023 0
Ending balance 11,440 12,861
Exercisable at end of period $ 7,363 $ 7,200