Quarterly report pursuant to Section 13 or 15(d)

Stock-based Compensation - Purchase Plan (Details)

v3.10.0.1
Stock-based Compensation - Purchase Plan (Details) - Purchase Plan
$ in Millions
9 Months Ended
Sep. 30, 2018
USD ($)
item
shares
Sep. 30, 2017
Additional disclosures    
Award offering period 24 months  
Number of purchase periods per award offering period | item 4  
Award purchase period 6 months  
Purchase price expressed as a percentage of fair market value of common stock on the purchase date 85.00%  
Purchase price expressed as a percentage of fair market value of common stock on the first day of the offering period 85.00%  
Shares reserved for future issuance | shares 1,790,451  
Unrecognized compensation cost related to purchase plan | $ $ 1.6  
Weighted-average assumptions relating to Purchase Plan    
Risk-free interest rate (as a percent) 2.40% 0.60%
Expected term (in years) 1 year 3 months 18 days 1 year 9 months 18 days
Dividend yield (as a percent) 0.00% 0.00%
Expected volatility (as a percent) 66.20% 64.60%