Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans - Additional Information (Details)

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Equity Incentive Plans - Additional Information (Details)
1 Months Ended 12 Months Ended
Jan. 01, 2018
shares
May 31, 2017
shares
Dec. 31, 2018
USD ($)
Participant
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance     2,343,087    
Unvested options resulting from early exercises     0 0 0
Aggregate intrinsic value of options exercised | $     $ 12,600,000 $ 800,000 $ 23,000,000,000
Total intrinsic value of all outstanding options | $     19,300,000 15,900,000 2,500,000
Total unrecognized stock-based compensation cost related to unvested stock options | $     $ 3,300,000 $ 800,000  
Total unrecognized stock-based compensation cost related to unvested stock options, recognized ratably over a weighted-average period     3 years 3 months 18 days 3 years 2 months 12 days  
Cash received from exercise of stock options | $     $ 550,000 $ 55,000 $ 25,000
Income tax benefits from stock-based compensation | $     $ 0    
Restricted Stock Unit          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period     12 months    
Total unrecognized stock-based compensation cost related to unvested stock options, recognized ratably over a weighted-average period     2 years 8 months 12 days 4 months 24 days  
Number of Units, Granted     92,883    
Grant Date Fair Value, Granted | $ / shares     $ 17.87    
Total unrecognized stock-based compensation cost related RSUs | $     $ 1,400,000 $ 300,000  
Restricted Stock Unit | Vesting Rate, Year One          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Granted restricted stock units of common stock, vesting percentage     35.00%    
Restricted Stock Unit | Vesting Rate, Year Two          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Granted restricted stock units of common stock, vesting percentage     21.667%    
Restricted Stock Unit | Vesting Rate, Year Three          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Granted restricted stock units of common stock, vesting percentage     21.667%    
Restricted Stock Unit | Vesting Rate, Year Four          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Granted restricted stock units of common stock, vesting percentage     21.667%    
Restricted Stock Unit | Director          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Units, Granted     17,881 47,312  
Grant Date Fair Value, Granted | $ / shares     $ 28.45    
Minimum | Restricted Stock Unit          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       7 years  
Minimum | Restricted Stock Unit | Director          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Grant Date Fair Value, Granted | $ / shares       $ 11.50  
Maximum | Restricted Stock Unit          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period       10 months  
Maximum | Restricted Stock Unit | Director          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Grant Date Fair Value, Granted | $ / shares       $ 16.96  
2017 Equity Incentive Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance   2,413,659      
Number of shares available for future grant   900,000 1,248,424    
Shares of common stock reserved for issuance, automatic annual increase initiation date   Jan. 01, 2018      
Percentage of number of shares of common stock outstanding       5.00%  
Increase in common stock reserved for issuance 491,356        
2017 Equity Incentive Plan | Shares under 2005 Plan that would have otherwise been returned to 2005 Plan | Maximum          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance   1,314,752      
Incentive Stock Options          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Ownership percentage, minimum     10.00%    
Incentive Stock Options | Minimum          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Percentage of fair value of common stock granted to employees     110.00%    
2005 Plan and 2017 Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Vesting period     4 years    
2005 Plan and 2017 Plan | Maximum          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Expiration period     10 years    
2017 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance     200,000    
Number of shares available for future grant     232,262    
Percentage of number of shares of common stock outstanding       2.00%  
Increase in common stock reserved for issuance 150,000        
Percentage of fair market value of common stock on purchase date of the first day of IPO   85.00%      
Percentage of fair market value of common stock on purchase date   85.00%      
Purchase of common stock under ESPP, Description     The 2017 ESPP allows eligible employees to purchase shares of the Company’s common stock in an offering at a discount of the then-current trading price, up to the lesser of (1) 85% of the fair market value of the common stock on the first day of the IPO or (2) 85% of the fair market value of the common stock on the purchase date. The 2017 ESPP permits the maximum discounted purchase price permitted under U.S. tax rules, including a “lookback.”    
Initial offering period in length     24 months    
Number of participant have the right to purchase shares of common stock | Participant     0    
Fair Market Value Of Common Stock | $     $ 25,000    
Periodic increment of common stock reserved for future issuance     150,000    
Shares issued under ESPP     83,605