Annual report pursuant to Section 13 and 15(d)

Share-based Compensation - Schedule of Restricted Stock Awards under 2013 Plan (Detail)

v3.8.0.1
Share-based Compensation - Schedule of Restricted Stock Awards under 2013 Plan (Detail) - Restricted stock awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Number of Shares, Restricted stock at beginning of period 343,958 137,114 173,222
Number of Shares, Restricted stock granted 127,239 287,179 58,092
Number of Shares, Restricted stock vested (139,298) (77,515) (68,017)
Number of Shares, Restricted stock forfeited (14,116) (2,820) (26,183)
Number of Shares, Restricted stock at end of period 317,783 343,958 137,114
Weighted-Average Grant Date Fair Value Per Share, Restricted stock at beginning of period (in usd per share) $ 16.60 $ 20.74 $ 19.58
Weighted-Average Grant Date Fair Value Per Share, Restricted stock granted (in usd per share) 31.06 15.52 22.53
Weighted-Average Grant Date Fair Value Per Share, Restricted stock vested (in usd per share) 18.73 19.75 19.16
Weighted-Average Grant Date Fair Value Per Share, Restricted stock forfeited (in usd per share) 24.73 21.58 21.16
Weighted-Average Grant Date Fair Value Per Share, Restricted stock at end of period (in usd per share) $ 21.09 $ 16.60 $ 20.74