Annual report pursuant to Section 13 and 15(d)

STOCK INCENTIVE AND STOCK OPTION PLANS (Details 2)

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STOCK INCENTIVE AND STOCK OPTION PLANS (Details 2) (USD $)
 12 Months Ended
Dec. 31, 2011
Y
Dec. 31, 2010
Y
Dec. 31, 2009
Y
Stock option plan activity      
Balance, at the beginning of the period (in shares) 1,073,595 896,830 440,080
Granted (in shares) 316,159 387,250 598,510
Exercised (in shares) (134,520) (195,530) (117,830)
Forfeited (in shares) (12,197) (8,555) (3,530)
Expired (in shares)   (6,400) (20,400)
Balance, at the end of the period (in shares) 1,243,037 1,073,595 896,830
Exercisable (in shares) 721,210 222,110 376,450
Weighted-average Exercise Price at the beginning of the period (in dollars per share) $ 37.92 $ 22.55 $ 16.14
Weighted-average Exercise Price Granted (in dollars per share) $ 115.71 $ 62.74 $ 25.31
Weighted-average Exercise Price Exercised (in dollars per share) $ 23.93 $ 17.36 $ 14.66
Weighted-average Exercise Price Forfeited (in dollars per share) $ 57.68 $ 41.54 $ 25.05
Weighted-average Exercise Price Expired (in dollars per share)   $ 9.33 $ 10.63
Weighted-average Exercise Price at the end of the period (in dollars per share) $ 59.02 $ 37.92 $ 22.55
Weighted-average Exercise Price Exercisable (in dollars per share) $ 38.75 $ 26.36 $ 18.50
Weighted-average remaining contractual life of options outstanding (in years) 7.29    
Weighted-average remaining contractual life of options exercisable (in years) 6.25 5.40 4.82
Aggregate intrinsic value of options outstanding (in dollars) $ 45,224,497    
Aggregate intrinsic value of options exercisable (in dollars) 37,526,500 18,683,972 10,709,436
Weighted average grant date fair value of options granted (in dollars per share) $ 51.23 $ 27.45 $ 10.57
Total intrinsic value of options exercised (in dollars) $ 12,000,000 $ 13,000,000 $ 3,000,000