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Stockholders' Equity - Stock Options (Details) - shares
9 Months Ended
Feb. 13, 2018
Jan. 04, 2018
Jan. 01, 2018
Sep. 30, 2018
Sep. 08, 2017
Jul. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Percentage increase of authorized shares     4.00%      
Options to purchase common stock | 2017 Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Maximum shares authorized (in shares)         400,000 400,000
Award vesting period       4 years    
Expiration period 10 years 10 years   10 years    
Annual additional options authorized (in shares)     101,431 101,431