Stock-Based Compensation - Exercise Price Range of Options Outstanding and Exercisable (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Options Outstanding
Shares (in shares)	11,703
Options Exercisable
Shares (in shares)	10,346
Exercise Price Range $0.06 to $0.40
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Share-based payments arrangement, option, exercise price range, lower range limit (in dollars per share) | $ / shares	$ 0.06
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 0.40
Options Outstanding
Shares (in shares)	2,593
Weighted Average Remaining Contractual Life  (in Years)	6 years 5 months 15 days
Options Exercisable
Shares (in shares)	2,590
Weighted Average Remaining Contractual Life  (in Years)	6 years 5 months 15 days
Exercise Price Range $1.55 to $2.33
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Share-based payments arrangement, option, exercise price range, lower range limit (in dollars per share) | $ / shares	$ 1.55
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 2.33
Options Outstanding
Shares (in shares)	3,047
Weighted Average Remaining Contractual Life  (in Years)	7 years 7 months 20 days
Options Exercisable
Shares (in shares)	2,910
Weighted Average Remaining Contractual Life  (in Years)	7 years 7 months 20 days
Exercise Price Range $2.43 to $3.65
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Share-based payments arrangement, option, exercise price range, lower range limit (in dollars per share) | $ / shares	$ 2.43
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 3.65
Options Outstanding
Shares (in shares)	3,254
Weighted Average Remaining Contractual Life  (in Years)	8 years 8 months 1 day
Options Exercisable
Shares (in shares)	3,254
Weighted Average Remaining Contractual Life  (in Years)	8 years 8 months 1 day
Exercise Price Range $8.17 to $12.26
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Share-based payments arrangement, option, exercise price range, lower range limit (in dollars per share) | $ / shares	$ 8.17
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 12.26
Options Outstanding
Shares (in shares)	1,871
Weighted Average Remaining Contractual Life  (in Years)	9 years 3 months 21 days
Options Exercisable
Shares (in shares)	1,490
Weighted Average Remaining Contractual Life  (in Years)	9 years 2 months 23 days
Exercise Price Range $12.79 to $19.19
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Share-based payments arrangement, option, exercise price range, lower range limit (in dollars per share) | $ / shares	$ 12.79
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 19.19
Options Outstanding
Shares (in shares)	938
Weighted Average Remaining Contractual Life  (in Years)	9 years 6 months 18 days
Options Exercisable
Shares (in shares)	102
Weighted Average Remaining Contractual Life  (in Years)	9 years 5 months 12 days