Stock-Based Compensation Expense and Employee Benefit Plans - Unvested Restricted Stock Unit Activity (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Unvested Restricted Stock Unit Activity
Unvested balance (in shares) | shares	6,418,788
Granted (in shares) | shares	5,566,751
Vested (in shares) | shares	(2,533,027)
Forfeited (in shares) | shares	(1,184,222)
Unvested balance (in shares) | shares	8,268,290
Weighted Average Grant Date Fair Value
Unvested balance (in dollars per share) | $ / shares	$ 13.71
Granted (in dollars per share) | $ / shares	24.27
Vested (in dollars per share) | $ / shares	16.65
Forfeited (in dollars per share) | $ / shares	16.37
Unvested balance (in dollars per share) | $ / shares	$ 19.54