Annual report pursuant to Section 13 and 15(d)

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

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Retirement and Long-Term Incentive Plans - Summary of Status of Restricted Stock Awards (Detail) - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Number of Shares      
Number of restricted shares, beginning balance 107,840 178,950 143,150
Number of shares, granted 215,034 6,000 100,150
Number of shares, vested (41,112) (45,356) (38,188)
Number of shares, forfeited (18,798) (31,754) (26,162)
Number of restricted shares, ending balance 262,964.000 107,840 178,950
Weighted Average Grant-Date Fair Value Per Share      
Weighted-average grant-date fair value, restricted shares, beginning balance $ 24.27 $ 24.00 $ 24.28
Weighted-average grant-date fair value per share, granted 16.33 23.19 23.22
Weighted-average grant-date fair value per share, vested 22.04 23.35 23.14
Weighted-average grant-date fair value per share, forfeited 21.39 23.85 23.82
Weighted-average grant-date fair value, restricted shares, ending balance $ 18.33 $ 24.27 $ 24.00