Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Plans - Employee Stock Purchase Plan - Additional Information (Detail)

v3.8.0.1
Stock-Based Compensation Plans - Employee Stock Purchase Plan - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2017
USD ($)
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Common stock shares available for issuance 5,459,345
ESPP description The ESPP Plan provides for annual increases in the number of shares available for issuance under the ESPP, equal to the least of (i) 366,667 shares, (ii) 1% of the outstanding shares on such date, or (iii) an amount determined by the board. Pursuant to the provisions of the ESPP Plan, the board of directors determined a share reserve increase was not required in the prior years.
Unrecognized stock-based compensation expense | $ $ 20,360,000
Unrecognized stock-based compensation expenses recognition period 2 years 11 months 26 days
Employee Stock Purchase Plan [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
ESPP offering period description The offering periods generally start on the first trading day on or after May 15 and November 15 of each year.
Length of purchase intervals 6 months
ESPP discount rate 10.00%
Common stock reserved and available for issuance 366,667
Common stock shares available for issuance 258,949
Unrecognized stock-based compensation expense | $ $ 16,000
Unrecognized stock-based compensation expenses recognition period 1 month 13 days
Employee Stock Purchase Plan - Annual Available for Issuance Share Increase [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Common stock available for future issuance authorized annual share increase 366,667
Common stock available for future issuance authorized annual percentage increase 1.00%
ESPP description The ESPP Plan provides for annual increases in the number of shares available for issuance under the ESPP, equal to the least of (i) 366,667 shares, (ii) 1% of the outstanding shares on such date, or (iii) an amount determined by the board.