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Stock Option Activity (Detail) (USD $)
9 Months Ended
Sep. 30, 2011
Underlying Shares 
Outstanding at beginning of period7,710,102
Granted419,500
Exercised(838,307)
Outstanding at end of period7,291,295
Exercisable at end of period6,112,320
Weighted Average Exercise Price 
Outstanding at beginning of period$ 19.58
Granted$ 30.28
Exercised$ 16.75
Outstanding at end of period$ 20.52
Exercisable at end of period$ 20.63