Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Summary of Changes In Restricted Stock (Detail)

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Share-based Compensation - Summary of Changes In Restricted Stock (Detail) - Restricted Stock [Member] - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Shares      
Nonvested stock, Beginning balance, Shares (in shares) 170,780 197,324 203,258
Granted (in shares) 122,978 96,724 119,601
Vested (in shares) (125,410) (117,852) (118,097)
Forfeited (in shares) (17,871) (5,416) (7,438)
Nonvested stock, Ending balance, Shares (in shares) 150,477 170,780 197,324
Weighted-Average Grant-Date Fair Value      
Nonvested stock, Beginning balance (in dollars per share) $ 27.43 $ 21.06 $ 14.53
Granted (in dollars per share) 29.70 33.11 27.00
Vested (in dollars per share) 25.88 21.47 16.05
Forfeited (in dollars per share) 30.22 26.29 17.59
Nonvested stock, Ending balance (in dollars per share) $ 30.25 $ 27.43 $ 21.06