Stock-Based Compensation - FV of employee stock options (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options to purchase common stock
Weighted average assumptions for estimated fair value of employee stock options
Common stock fair value per share minimum	30.65	20.69	29.96
Common stock fair value per share maximum	49.47	45.91	44.19
Expected volatility, low end of range (as a percent)	53.91%	52.93%	60.67%
Expected volatility, high end of range (as a percent)	56.82%	58.95%	61.33%
Risk-free interest rate, low end of range (as a percent)	0.47%	0.29%	1.37%
Risk-free interest rate, high end of range (as a percent)	1.33%	1.71%	2.60%
Compensation expense
Unamortized compensation expense related to unvested awards	$ 54.5	$ 48.9
Period to recognize unamortized compensation expense	2 years 7 months 13 days
Options to purchase common stock \| Minimum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	6 years	5 years 2 months 23 days	5 years 2 months 23 days
Options to purchase common stock \| Maximum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	7 years 7 months 24 days	7 years 7 months 24 days	6 years 7 months 2 days
Employee stock purchase plan
Weighted average assumptions for estimated fair value of employee stock options
Expected volatility, low end of range (as a percent)	46.08%	50.77%	50.77%
Expected volatility, high end of range (as a percent)	66.37%	66.37%	71.37%
Risk-free interest rate, low end of range (as a percent)	0.04%	0.09%	1.47%
Risk-free interest rate, high end of range (as a percent)	1.65%	1.65%	2.70%
Compensation expense
Unamortized compensation expense related to unvested awards	$ 2.3	$ 0.9
Period to recognize unamortized compensation expense	1 year 11 months 8 days
Employee stock purchase plan \| Minimum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	6 months	6 months	6 months
Employee stock purchase plan \| Maximum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	2 years	2 years	2 years

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The estimated fair value of the entity's common stock at the date of grant of stock options, used as an input in calculating the grant date fair value of the options maximum.

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The minimum estimated fair value of the entity's common stock at the date of grant of stock options, used as an input in calculating the grant date fair value of the options.

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