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Summary of Performance Stock Unit Activity (Detail) (Performance Stock Unit Activity, USD $)
3 Months Ended
Mar. 31, 2014
Performance Stock Unit Activity
 
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]  
Unvested Shares, Beginning Balance 149,389
Granted, Shares 46,242
Performance adjustments, Shares 41,428
Vested, Shares (88,996)
Unvested Shares, Ending Balance 148,063.000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]  
Unvested Weighted Average Grant Date Fair value, Beginning Balance $ 46.32
Granted, Weighted Average Grant Date Fair Value $ 57.42
Performance adjustments, Weighted Average Grant Date Fair Value $ 39.42
Vested, Weighted Average Grant Date Fair Value $ 39.11
Unvested Weighted Average Grant Date Fair value, Ending Balance $ 52.20