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Stock-Based Compensation - Details of Nonvested Restricted Stock Units Activity (Detail) - Restricted Stock Units (RSUs) [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Units Outstanding, Beginning Balance, Nonvested 197,838    
Number of Units, Granted 111,652    
Number of Units, Vested (94,840)    
Number of Units, Canceled (19,988)    
Number of Units, Accrued dividend equivalents 2,726    
Number of Units Outstanding, Ending Balance, Nonvested 197,388 197,838  
Weighted Average Grant-Date Fair Value, Nonvested, Beginning Balance $ 26.48    
Weighted Average Grant-Date Fair Value, Granted 36.35 $ 27.53 $ 25.72
Weighted Average Grant-Date Fair Value, Vested 27.72    
Weighted Average Grant-Date Fair Value, Canceled 31.52    
Weighted Average Grant-Date Fair Value, Accrued dividend equivalents 32.59    
Weighted Average Grant-Date Fair Value, Nonvested, Ending Balance 33.50 26.48  
Weighted average grant-date fair value of restricted shares granted $ 36.35 $ 27.53 $ 25.72
Weighted average grant-date fair value of shares vested (thousands) $ 2,629 $ 1,185 $ 1,122