Annual report pursuant to Section 13 and 15(d)

Summary of Restricted Stock Award Activity (Detail)

v3.8.0.1
Summary of Restricted Stock Award Activity (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of restricted stock unit awards that vested during the period 192,230 430,056 329,437
Fair value of restricted shares that vested during the period $ 8,172 $ 14,662 $ 14,424
Income tax benefit recognized upon vesting of share based awards 2,667 5,555 3,823
Compensation expense recognized during the period $ 8,384 $ 8,250 $ 9,600
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 97,115 213,984 123,769
Fair value of restricted shares that vested during the period $ 4,155 $ 7,260 $ 5,483
Accumulated dividends paid upon vesting of restricted stock unit awards 558 662 442
Income tax benefit recognized upon vesting of share based awards 1,745 3,049 2,303
Compensation expense recognized during the period $ 4,297 $ 5,144 $ 6,158