The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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

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Stock-Based Compensation and Employee Benefit Plans - Weighted-Average Assumptions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Stock options and awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		3.90%
Expected term (years)		6 years 1 month 6 days		6 years 1 month 6 days
Expected dividend yield		0.00%		0.00%
Expected volatility		93.90%
Stock options and awards \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate				3.90%
Expected volatility				93.40%
Stock options and awards \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate				4.10%
Expected volatility				93.90%
Performance Shares \| 2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (minimum)	3.40%	3.80%	3.40%	3.80%
Risk-free interest rate (maximum)	4.20%	4.30%	4.20%	5.00%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility (minimum)	96.70%	80.50%	80.50%	66.20%
Expected volatility (maximum)	119.30%	115.20%	119.30%	115.20%
Performance Shares \| 2018 ESPP \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 months	6 months	6 months	6 months
Performance Shares \| 2018 ESPP \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	2 years	2 years	2 years	2 years