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Stock Plans - Summary of Performance Stock Unit Activity (Detail) - Performance Stock Unit Activity - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]        
Unvested Shares, Beginning Balance 149,389 143,961 149,389 137,672
Granted, Shares   87,256 46,242 53,357
Vested, Shares   (66,200) (91,696) (45,809)
Performance adjustments, Shares   16,447 41,428 4,169
Forfeited, Shares (1,402) (9,820)    
Unvested Shares, Ending Balance   171,644 143,961 149,389
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 (dollars per share) $ 46.32 $ 52.42 $ 46.32 $ 35.85
Granted, Weighted Average Grant Date Fair Value (dollars per share)   41.99 57.42 57.58
Vested, Weighted Average Grant Date Fair Value (dollars per share)   41.75 39.19 26.08
Performance adjustments, Weighted Average Grant Date Fair value (dollars per share)   41.45 39.42 25.84
Forfeited, Weighted Average Grant Date Fair Value (dollars per share) $ 48.85 51.51    
Unvested Weighted Average Grant Date Fair Value, Ending Balance (dollars per share)   $ 50.24 $ 52.42 $ 46.32