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, 2017
Sep. 30, 2016
Restricted Stock    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted stock unit awards that vested during the period 192,152  
Fair value of restricted shares that vested during the period $ 8,169 $ 14,662
Compensation expense recognized during the period 6,298 6,551
Income tax benefit recognized upon vesting of restricted stock awards $ 2,665 $ 5,555
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 97,115 213,984
Fair value of restricted shares that vested during the period $ 4,155 $ 7,260
Accumulated dividends paid upon vesting of restricted stock unit awards 313 662
Compensation expense recognized during the period 3,189 3,696
Income tax benefit recognized upon vesting of restricted stock awards $ 1,745 $ 3,049