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Stockholders' Equity - Stock-based Compensation Employee Stock Purchase Plan Fair Value Assumptions (Details) - Employee Stock Purchase Plan - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Class of Stock [Line Items]        
Expected term (in years) 1 year 2 months 12 days 1 year 1 year 1 month 6 days 1 year
Expected volatility 51.10% 71.70% 52.70% 55.00%
Risk-free interest rate 0.10% 0.10% 0.10% 0.90%
Expected dividends 0.00% 0.00% 0.00% 0.00%
Weighted average fair value at grant date (in usd per share) $ 257.89 $ 117.32 $ 246.84 $ 96.94