Annual report pursuant to Section 13 and 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) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Common stock shares available for issuance 5,586,917  
Unrecognized stock-based compensation expense $ 20,317,000  
Unrecognized stock-based compensation expenses recognition period 2 years 10 months 10 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 246,895 277,104
Unrecognized stock-based compensation expense $ 58,000  
Unrecognized stock-based compensation expenses recognition period 4 months 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 2013 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.