Quarterly report pursuant to Section 13 or 15(d)

Equity Incentive Plans - Additional Information (Details)

v3.19.2
Equity Incentive Plans - Additional Information (Details) - USD ($)
1 Months Ended 6 Months Ended 12 Months Ended
Jan. 01, 2019
May 31, 2017
Jun. 30, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted Stock Unit          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Units, Granted     39,597    
Vesting period     4 years    
Grant Date Fair Value, Granted     $ 44.95    
Restricted Stock Unit | Subject to Certain Financial Milestones          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Units, Granted     8,031    
Grant Date Fair Value, Granted     $ 43.58    
Granted restricted stock units of common stock, vesting percentage     100.00%    
Restricted Stock Unit | Directors          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Number of Units, Granted     14,755    
Grant Date Fair Value, Granted     $ 41.79    
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 1,669,522    
Shares of common stock reserved for issuance, automatic annual increase initiation date   Jan. 01, 2018      
Shares of common stock reserved for issuance, automatic annual increase end date   Jan. 01, 2027      
Percentage of number of shares of common stock outstanding       5.00% 5.00%
Increase in common stock reserved for issuance 543,236        
2017 Equity Incentive Plan | Shares under 2005 Plan that would have otherwise been returned to 2005 Plan | Maximum [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance   1,314,752      
2017 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Common stock reserved for issuance     200,000    
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   85.00%      
Percentage of fair market value of common stock on purchase date of the first day of IPO   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     June 2017 to June 2019    
Maximum amount of fair value of common stock by participant     $ 25,000    
Periodic increment of common stock reserved for future issuance     150,000    
Shares issued under ESPP     53,508