Stock-Based Compensation Expense - Summary of Restricted Stock and Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Shares
Unvested balance, Beginning balance (in shares) | shares	2,936,924
Granted (in shares) | shares	1,618,363
Vested (in shares) | shares	(1,092,477)
Forfeited (in shares) | shares	(201,187)
Unvested balance, Ending balance (in shares) | shares	3,261,623
Weighted-Average Grant Date Fair Value
Unvested balance, Beginning balance (in dollars per share) | $ / shares	$ 32.43
Granted (in dollars per share) | $ / shares	56.56
Vested (in dollars per share) | $ / shares	33.10
Forfeited (in dollars per share) | $ / shares	39.92
Unvested balance, Ending Balance (in dollars per share) | $ / shares	$ 43.74