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Equity Plans - Schedule of Activity under Stock Option Plan (Detail) - 2007 Stock Option Plan [Member] - USD ($)
$ / shares in Units, $ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options Granted [Roll Forward]    
Options Available for Grant, Beginning balance 164,328  
Options Available for Grant, Number of Additional Shares Authorized 668,891  
Options Available for Grant, Options granted (403,000)  
Options Available for Grant, Options exercised 0  
Options Available for Grant, Options Forfeited 85,930  
Options Available for Grant, Ending balance 516,149 164,328
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]    
Number of Options Outstanding, Beginning balance 2,393,829  
Number of Options Outstanding, Options granted 403,000  
Number of Options Outstanding, Options exercised (173,155)  
Number of Options Outstanding, Options Forfeited (85,930)  
Number of Options Outstanding, Ending balance 2,537,744 2,393,829
Number of Options Outstanding, Options exercisable 811,539  
Number of Options Outstanding, Options vested and expected to vest 2,537,744  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]    
Weighted-Average Exercise Price Per Share, Beginning balance $ 10.39  
Weighted-Average Exercise Price Per Share, Options granted 12.08  
Weighted-Average Exercise Price Per Share, Options exercised 1.50  
Weighted Average Exercise Price, Options Forfeited 16.79  
Weighted-Average Exercise Price Per Share, Ending balance 11.05 $ 10.39
Weighted-Average Exercise Price Per Share, Options exercisable 8.72  
Weighted-Average Exercise Price Per Share, Options vested and expected to vest $ 11.05  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]    
Weighted-Average Remaining Contractual Life (years) 8 years 6 months 18 days 8 years 9 months 15 days
Weighted-Average Remaining Contractual Life (years), Options exercisable 8 years 11 days  
Weighted-Average Remaining Contractual Life (years), Options vested and expected to vest 8 years 6 months 18 days  
Aggregate Intrinsic Value, Options Outstanding $ 20.2  
Aggregate Intrinsic Value, Options exercisable 8.2  
Aggregate Intrinsic Value, Options vested and expected to vest $ 20.2