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Common Stock and Share-Based Compensation - Summary Options Outstanding and Exercisable (Detail)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
8.96 to 10.44  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 88,451
Weighted- Average Remaining Contractual Life (in years) 3 years 8 months 9 days
Weighted-Average Exercise Price (USD per share) $ 9.77
Exercise price range, lower limit (USD per share) 8.96
Exercise price range, upper limit (USD per share) $ 10.44
12.60  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 69,423
Weighted- Average Remaining Contractual Life (in years) 2 years 22 days
Weighted-Average Exercise Price (USD per share) $ 12.60
Exercise price range, lower limit (USD per share) $ 12.60
13.30 to 16.98  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 74,044
Weighted- Average Remaining Contractual Life (in years) 1 year 6 months 4 days
Weighted-Average Exercise Price (USD per share) $ 15.09
Exercise price range, lower limit (USD per share) 13.30
Exercise price range, upper limit (USD per share) $ 16.98
17.36  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 222,184
Weighted- Average Remaining Contractual Life (in years) 1 year 29 days
Weighted-Average Exercise Price (USD per share) $ 17.36
Exercise price range, upper limit (USD per share) $ 17.36
17.48 to 21.14  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 23,563
Weighted- Average Remaining Contractual Life (in years) 7 months 10 days
Weighted-Average Exercise Price (USD per share) $ 18.82
Exercise price range, lower limit (USD per share) 17.48
Exercise price range, upper limit (USD per share) $ 21.14
21.96  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 221,936
Weighted- Average Remaining Contractual Life (in years) 15 days
Weighted-Average Exercise Price (USD per share) $ 21.96
Exercise price range, upper limit (USD per share) $ 21.96
24.60  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number Outstanding (shares) | shares 866
Weighted- Average Remaining Contractual Life (in years) 1 month 2 days
Weighted-Average Exercise Price (USD per share) $ 24.60
Exercise price range, upper limit (USD per share) $ 24.60