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Stock-based Compensation - Summary of Restricted Stock Units Activity (Detail) (Restricted Stock Units [Member], USD $)
3 Months Ended
Mar. 31, 2013
Restricted Stock Units [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of Shares, Beginning Balance 292,057
Number of Shares, Granted 30,719
Number of Shares, Forfeited (8,627)
Number of Shares, Settled (69,157)
Number of Shares, Ending Balance 244,992
Weighted Average Grant Date Fair Value, Beginning Balance $ 57.89
Weighted Average Grant Date Fair Value, Granted $ 185.75
Weighted Average Grant Date Fair Value, Forfeited $ 61.85
Weighted Average Grant Date Fair Value, Settled $ 42.33
Weighted Average Grant Date Fair Value, Ending Balance $ 85.37