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Stock-Based Compensation - Summary of Performance Share Units (Detail) (USD $)
9 Months Ended
Sep. 30, 2013
Weighted Average Grant Date Fair Value per Unit (in dollars per share)  
Vested, Weighted Average Grant Date Fair Value per Unit $ 0.00
Performance Share Units [Member]
 
PSUs (in shares)  
Non-vested shares outstanding, Beginning Balance 155,220
Granted 135,620
Vested   
Forfeited (21,540)
Non-vested shares outstanding, Ending Balance 269,300
Weighted Average Grant Date Fair Value per Unit (in dollars per share)  
Non-vested PSUs outstanding, Beginning Balance, Weighted Average Grant Date Fair Value per Unit $ 26.22
Granted, Weighted Average Grant Date Fair Value per Unit $ 42.01
Forfeited, Weighted Average Grant Date Fair Value per Unit $ 32.89
Non-vested PSUs outstanding, Ending Balance, Weighted Average Grant Date Fair Value per Unit $ 33.64