Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation - Purchase Plan (Details)

v3.19.1
Stock-Based Compensation - Purchase Plan (Details) - Purchase Plan
3 Months Ended
Mar. 31, 2019
USD ($)
item
shares
Mar. 31, 2018
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%  
Total incremental fair value for the Purchase Plan reset $ 879,000  
Shares reserved for future issuance | shares 1,331,584  
Unrecognized compensation cost related to purchase plan $ 1,500,000  
Weighted-average assumptions relating to Purchase Plan    
Risk-free interest rate (as a percent) 2.70% 0.60%
Expected term (in years) 1 year 6 months 2 years
Dividend yield (as a percent) 0.00% 0.00%
Expected volatility (as a percent) 62.60% 63.80%