Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation - Schedule of Restricted Stock Awards (Detail)

v3.8.0.1
Share-Based Compensation - Schedule of Restricted Stock Awards (Detail) - Restricted stock awards [Member]
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Vesting period 3 years
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 | shares 317,783
Number of Shares, Restricted stock granted | shares 97,724
Number of Shares, Restricted stock vested | shares (52,913)
Number of Shares, Restricted stock forfeited | shares (38,498)
Number of Shares, Restricted stock at end of period | shares 324,096
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]  
Weighted-Average Grant Date Fair Value Per Share, Restricted stock at beginning of period (in usd per share) | $ / shares $ 21.09
Weighted-Average Grant Date Fair Value Per Share, Restricted stock granted (in usd per share) | $ / shares 24.08
Weighted-Average Grant Date Fair Value Per Share, Restricted stock vested (in usd per share) | $ / shares 26.86
Weighted-Average Grant Date Fair Value Per Share, Restricted stock forfeited (in usd per share) | $ / shares 9.97
Weighted-Average Grant Date Fair Value Per Share, Restricted stock at end of period (in usd per share) | $ / shares $ 22.38