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Activity in Nonvested Restricted Stock Unit Awards (Detail) (Restricted Stock Units, USD $)
12 Months Ended
Dec. 31, 2012
Restricted Stock Units
 
Share Based Compensation [Line Items]  
Number of shares outstanding, beginning balance 547,272
Number of options, granted 152,128
Number of shares, vested (71,230)
Number of shares, forfeited (94,013)
Number of shares outstanding, ending balance 534,157
Weighted average grant date fair value outstanding, beginning balance $ 82.36
Weighted average grant date fair value, granted $ 90.38
Weighted average grant date fair value, vested $ 76.30
Weighted average grant date fair value, forfeited $ 83.87
Weighted average grant date fair value outstanding, ending balance $ 85.17