Stock-Based Compensation - Employee and Director Stock Option Activity (Details) - Employees, Directors and Consultants - $ / shares	9 Months Ended
Sep. 30, 2021
Number of Shares
Beginning balance (in shares)	3,616,314
Granted (in shares)	738,628
Exercised (in shares)	(395,181)
Forfeited (in shares)	(472,740)
Expired (in shares)	(271)
Ending balance (in shares)	3,486,750
Vested (in shares)	1,115,549
Exercisable (in shares)	1,115,549
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 14.66
Granted (in dollars per share)	24.08
Exercised (in dollars per share)	14.13
Forfeited (in dollars per share)	14.27
Expired (in dollars per share)	48.00
Ending balance (in dollars per share)	16.77
Vested (in dollars per share)	14.51
Exercisable (in dollars per share)	$ 14.51

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.