Stock-Based Compensation - Summary of Activity under Restricted Stock Unit Plans (Details) - RSUs issued and outstanding - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of RSUs Outstanding
Unvested balance - beginning balance (in shares)	2,503,182
Granted (in shares)	5,750,034
Vested (in shares)	(1,590,225)
Forfeited/canceled (in shares)	(1,094,766)
Unvested balance - ending balance (in shares)	5,568,225	2,503,182
Weighted-Average Grant Date Fair Value
Unvested balance - beginning balance (in dollars per share)	$ 15.82
Granted (in dollars per share)	10.96	$ 16.15	$ 15.00
Vested (in dollars per share)	13.15
Forfeited/canceled (in dollars per share)	12.70
Unvested balance - ending balance (in dollars per share)	$ 12.20	$ 15.82