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
3 Months Ended
Mar. 31, 2018
Mar. 31, 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 202,341  
Fair value of restricted shares that vested during the period $ 7,807 $ 6,013
Compensation expense recognized during the period 2,375 2,127
Income tax benefit recognized upon vesting of restricted stock awards $ 1,399 $ 1,972
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 125,063 97,115
Fair value of restricted shares that vested during the period $ 3,594 $ 4,155
Accumulated dividends paid upon vesting of restricted stock unit awards 522 68
Compensation expense recognized during the period 1,051 1,114
Income tax benefit recognized upon vesting of restricted stock awards $ 723 $ 1,745