Stock-Based Compensation Expense - Summary of Restricted Stock and Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Shares
Unvested balance, Beginning balance (in shares) | shares	2,941,914
Granted (in shares) | shares	1,867,104
Vested (in shares) | shares	(1,251,639)
Forfeited (in shares) | shares	(316,711)
Unvested balance, Ending balance (in shares) | shares	3,240,668
Weighted-Average Grant Date Fair Value
Unvested balance, Beginning balance (in dollars per share) | $ / shares	$ 45.86
Granted (in dollars per share) | $ / shares	91.26
Vested (in dollars per share) | $ / shares	45.13
Forfeited (in dollars per share) | $ / shares	63.22
Unvested balance, Ending Balance (in dollars per share) | $ / shares	$ 70.60