Annual report pursuant to Section 13 and 15(d)

Summary of Restricted Share Units Activity (Detail)

v3.8.0.1
Summary of Restricted Share Units Activity (Detail) - Restricted Share Units
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares  
Number of Restricted Shares, Beginning Balance | shares 132,517
Number of Restricted Shares, Shares Granted | shares 351,449
Number of Restricted Shares, Shares Vested | shares (227,689)
Number of Restricted Shares, Shares Forfeited | shares (13,593)
Number of Restricted Shares, Ending Balance | shares 242,684
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value  
Weighted Average Grant Date Fair Value Per Share, Beginning Balance | $ / shares $ 6.84
Weighted Average Grant Date Fair Value Per Share, Shares Granted | $ / shares 7.20
Weighted Average Grant Date Fair Value Per Share, Shares Vested | $ / shares 7.03
Weighted Average Grant Date Fair Value Per Share, Shares Forfeited | $ / shares 7.20
Weighted Average Grant Date Fair Value Per Share, Ending Balance | $ / shares $ 7.17