Annual report pursuant to Section 13 and 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
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2008
Shares, Outstanding at beginning of year 1,073,800 881,000 863,500  
Shares, Granted 45,500 233,500 37,500  
Shares, Exercised (288,130) (40,700) (10,000)  
Shares, Forfeited (14,670) 0 (10,000)  
Shares, Outstanding at end of year 816,500 1,073,800 881,000  
Shares, Ending Exercisable 412,825 442,940 272,627  
Weighted Average Exercise Price, Outstanding at beginning of year $ 18.33 $ 15.65 $ 15.17 $ 14.70
Weighted Average Exercise Price, Granted $ 30.00 $ 27.16 $ 25.00  
Weighted Average Exercise Price, Exercised $ 12.71 $ 10.53 $ 10.00  
Weighted Average Exercise Price, Forfeited $ 24.54 $ 15.00 $ 15.00  
Weighted Average Exercise Price, Outstanding at end of year $ 20.87 $ 18.33 $ 15.65 $ 14.70
Weighted Average Exercise Price, Ending Exercisable $ 14.03 $ 13.19 $ 11.96  
Weighted Average Remaining Contractual Term (years), Outstanding at beginning of year 6 years 6 years 10 months 24 days 6 years 9 months 18 days 7 years 8 months 12 days
Weighted Average Remaining Contractual Term (years), Granted 9 years 3 months 18 days 9 years 3 months 18 days 9 years 4 months 24 days  
Weighted Average Remaining Contractual Term (years), Exercised 2 years 4 months 24 days 3 years 9 months 18 days 0 years  
Weighted Average Remaining Contractual Term (years), Forfeited 0 years 0 years 0 years  
Outstanding at end of year 5 years 9 months 18 days 6 years 6 years 10 months 24 days 7 years 8 months 12 days
Weighted Average Remaining Contractual Term (years), Ending Exercisable 3 years 7 months 6 days 4 years 4 months 24 days 5 years 1 month 6 days  
Aggregate Intrinsic Value, Outstanding at beginning of year $ 12,508 $ 8,238 $ 8,483 $ 8,513
Aggregate Intrinsic Value, Granted 130 0 0  
Aggregate Intrinsic Value, Exercised 5,846 792 150  
Aggregate Intrinsic Value, Forfeited 0 0 0  
Aggregate Intrinsic Value, Outstanding at end of year 9,905 12,508 8,238 8,513
Aggregate Intrinsic Value, Ending Exercisable $ 7,831 $ 7,447 $ 3,555