Stock-Based Compensation Expense and Employee Benefit Plans - Number of Shares Available for Grant (Details)	6 Months Ended
	Jun. 30, 2021 shares
Options/ RSUs Available for Grant
Beginning balance (in shares)	20,233,754
Added to plan (in shares)	7,675,984
Granted (in shares)	(5,147,681)
Cancelled (in shares)	1,376,014
Expired (in shares)	(171,843)
Ending Balance (in shares)	23,966,228