Annual report pursuant to Section 13 and 15(d)

Long-Term Incentive Plans - Summary of Status of Restricted Stock Awards (Detail)

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Long-Term Incentive Plans - Summary of Status of Restricted Stock Awards (Detail) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Number of Shares      
Number of restricted shares, beginning balance 143,150    
Number of shares, granted 100,150 60,250 67,600
Number of shares, vested (38,188)    
Number of shares, forfeited (26,162)    
Number of restricted shares, ending balance 178,950 143,150  
Weighted Average Grant-Date Fair Value Per Share      
Weighted-average grant-date fair value, restricted shares, beginning balance $ 24.28    
Weighted-average grant-date fair value per share, granted $ 23.22 $ 23.53 $ 28.43
Weighted-average grant-date fair value per share, vested $ 23.14    
Weighted-average grant-date fair value per share, forfeited $ 23.82    
Weighted-average grant-date fair value, restricted shares, ending balance $ 24.00 $ 24.28