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Summary Information about Stock Options Outstanding (Detail)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
$4.36 - $7.20  
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Range of Exercise Prices, lower limit $ 4.36
Range of Exercise Prices, upper limit $ 7.20
Options Number Outstanding | shares 479,810
Options Outstanding Weighted Average Remaining Contractual Life (Years) 8 years 2 months 19 days
Options Outstanding Weighted Average Exercise Price $ 4.48
Options Number Exercisable | shares 285,359
Options Exercisable Weighted Average Exercise Price $ 4.57
$7.50 - $11.30  
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Range of Exercise Prices, lower limit 7.50
Range of Exercise Prices, upper limit $ 11.30
Options Number Outstanding | shares 162,394
Options Outstanding Weighted Average Remaining Contractual Life (Years) 5 years 11 months 12 days
Options Outstanding Weighted Average Exercise Price $ 9.27
Options Number Exercisable | shares 151,407
Options Exercisable Weighted Average Exercise Price $ 9.23
$12.00 - $19.70  
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Range of Exercise Prices, lower limit 12.00
Range of Exercise Prices, upper limit $ 19.70
Options Number Outstanding | shares 17,396
Options Outstanding Weighted Average Remaining Contractual Life (Years) 4 years 6 months
Options Outstanding Weighted Average Exercise Price $ 13.66
Options Number Exercisable | shares 17,396
Options Exercisable Weighted Average Exercise Price $ 13.66
$21.70 - $29.20  
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Range of Exercise Prices, lower limit 21.70
Range of Exercise Prices, upper limit $ 29.20
Options Number Outstanding | shares 12,841
Options Outstanding Weighted Average Remaining Contractual Life (Years) 3 years 3 months 11 days
Options Outstanding Weighted Average Exercise Price $ 25.35
Options Number Exercisable | shares 12,841
Options Exercisable Weighted Average Exercise Price $ 25.35
$4.36 - $29.20  
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Range of Exercise Prices, lower limit 4.36
Range of Exercise Prices, upper limit $ 29.20
Options Number Outstanding | shares 672,441
Options Number Exercisable | shares 467,003