Stock-Based Compensation - Exercise Price Range of Options Outstanding and Exercisable (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2021 $ / shares shares
Options Outstanding
Shares (in shares)	12,032
Options Exercisable
Shares (in shares)	10,798
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)	2,919
Weighted Average Remaining Contractual Life  (in Years)	6 years 6 months 21 days
Options Exercisable
Shares (in shares)	2,885
Weighted Average Remaining Contractual Life  (in Years)	6 years 6 months 21 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)	3,201
Weighted Average Remaining Contractual Life  (in Years)	7 years 10 months 13 days
Options Exercisable
Shares (in shares)	3,042
Weighted Average Remaining Contractual Life  (in Years)	7 years 10 months 13 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)	3,270
Weighted Average Remaining Contractual Life  (in Years)	8 years 10 months 28 days
Options Exercisable
Shares (in shares)	3,269
Weighted Average Remaining Contractual Life  (in Years)	8 years 10 months 28 days
Exercise Price Range $8.90 to $13.35
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	$ 8.90
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 13.35
Options Outstanding
Shares (in shares)	1,924
Weighted Average Remaining Contractual Life  (in Years)	9 years 5 months 15 days
Options Exercisable
Shares (in shares)	1,569
Weighted Average Remaining Contractual Life  (in Years)	9 years 5 months 1 day
Exercise Price Range $15.17 to $22.76
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	$ 13.90
Share-based payments arrangement, option, exercise price range, upper range limit (in dollars per share) | $ / shares	$ 20.85
Options Outstanding
Shares (in shares)	718
Weighted Average Remaining Contractual Life  (in Years)	9 years 9 months 25 days
Options Exercisable
Shares (in shares)	33
Weighted Average Remaining Contractual Life  (in Years)	9 years 8 months 23 days