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Equity and Stock-based Compensation - Employee Stock Purchase Plan - Additional information (Detail) - 2014 ESPP [Member] - shares
1 Months Ended 12 Months Ended
Sep. 30, 2014
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Purchase of common stock shares at discount 15.00%      
Percentage of fair value exercise price grant date 85.00%      
Number of common stock reserved for issuance 1,600,000      
Common stock reserved for future issuance, Description   The Company has reserved 1,600,000 shares of its common stock for issuance under the 2014 ESPP and shares reserved for issuance increases January 1 of each year commencing January 1, 2016 by the lesser of (i) a number of shares equal to 1% of the total number of outstanding shares of common stock on December 31 immediately prior to the date of increase; (ii) 1,200,000 shares or (iii) such number of shares as may be determined by the board of directors.    
Percentage of common stock reserved for future issuance 1.00%      
Increase in number of shares of common stock reserved for future issuance, shares 1,200,000      
Shares purchased by employees   230,317 250,834 266,720