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Stock-Based Compensation - Employee Stock Purchase Plan (Details) - 2014 ESPP - $ / shares
12 Months Ended
Apr. 22, 2014
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Stock-Based Compensation        
Length of purchase intervals under ESPP plan 6 months      
Percentage of purchase price per share (percent) 85.00%      
Maximum percentage of base salary allowable for employee share purchases (percent) 15.00%      
Maximum number of common stock permitted to be purchased by employees on any one purchase date under ESPP 5,000      
Maximum fair value of shares permitted to be purchased under ESPP (usd per share) $ 25,000      
Shares of common stock reserved for future issuance (shares)   685,720    
Valuation assumptions        
Volatility, minimum (percent)   60.00% 36.00% 42.00%
Volatility, maximum (percent)   93.00% 42.00% 52.00%
Risk-free interest rate, minimum (percent)   1.37% 1.13% 0.70%
Risk-free interest rate, maximum (percent)   2.86% 2.28% 1.10%
Expected life (in years)   6 months 6 months 6 months
Dividend yield (percent)   0.00% 0.00% 0.00%
Maximum        
Stock-Based Compensation        
Shares of common stock reserved for future issuance (shares) 2,000,000