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Summary of Option Activity (Detail)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Options Outstanding  
Options outstanding at December 31, 2016 | shares 882,748
Granted | shares 101,844
Exercised | shares (215,495)
Forfeited/cancelled | shares (34,157)
Options outstanding at December 31, 2017 | shares 734,940
Options exercisable at December 31, 2017 | shares 420,688
Vested and expected to vest at December 31, 2017 | shares 727,278 [1]
Weighted-Average Exercise Price Per Share  
Options outstanding at December 31, 2016 | $ / shares $ 16.88
Granted | $ / shares 33.38
Exercised | $ / shares 10.92
Forfeited/cancelled | $ / shares 20.23
Options outstanding at December 31, 2017 | $ / shares 20.80
Options exercisable at December 31, 2017 | $ / shares 15.86
Vested and expected to vest at December 31, 2017 | $ / shares $ 20.71 [1]
Weighted-Average Remaining Contractual Term (in years)  
Options outstanding at December 31, 2017 6 years 5 months 16 days
Options exercisable at December 31, 2017 5 years 3 months 11 days
Vested and expected to vest at December 31, 2017 6 years 5 months 9 days [1]
Aggregate Intrinsic Value  
Options outstanding at December 31, 2017 | $ $ 11,558
Options exercisable at December 31, 2017 | $ 8,720
Vested and expected to vest at December 31, 2017 | $ $ 11,472 [1]
[1] Represents the number of vested options as of December 31, 2017 plus the number of unvested options expected to vest as of December 31, 2017 based on the unvested outstanding options at December 31, 2017 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.