Quarterly report pursuant to Section 13 or 15(d)

Summary of Restricted Stock Award Activity (Detail)

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Summary of Restricted Stock Award Activity (Detail) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Restricted Stock    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted stock unit awards that vested during the period 242,945  
Fair value of restricted shares that vested during the period $ 7,815 $ 8,169
Compensation expense recognized during the period 7,266 6,298
Income tax benefit recognized upon vesting of restricted stock awards $ 1,751 $ 2,665
Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted stock unit awards that vested during the period 127,084 97,115
Fair value of restricted shares that vested during the period $ 4,846 $ 4,155
Accumulated dividends paid upon vesting of restricted stock unit awards 526 313
Compensation expense recognized during the period 3,098 3,189
Income tax benefit recognized upon vesting of restricted stock awards $ 740 $ 1,745