Stock-Based Compensation - Restricted Stock Units Activity (Details) - Restricted Stock Unit - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Restricted Stock Units
Restricted stock units, unvested, beginning balance (in shares)	1,941,155
Restricted stock units, granted (in shares)	1,186,899
Restricted stock units, vested (in shares)	(467,245)
Restricted stock units, forfeited (in shares)	(143,515)
Restricted stock units, unvested, ending balance (in shares)	2,517,294	1,941,155
Restricted stock units, vested and expected to vest (in shares)	2,517,294
Weighted- Average Fair Value at Date of Grant per Share
Weighted-average fair value at date of grant per share, beginning balance (in dollars per share)	$ 27,450
Weighted-average fair value at date of grant per share, granted (in dollars per share)	23.70
Weighted-average fair value at date of grant per share, vested (in dollars per share)	27.42
Weighted-average fair value at date of grant per share, forfeited (in dollars per share)	24.48
Weighted-average fair value at date of grant per share, ending balance (in dollars per share)	25.86	$ 27,450
Weighted-average fair value at date of grant per share, vested and expected to vest (in dollars per share)	$ 25.86
Weighted average remaining vesting life, unvested (in years)	1 year 10 months 13 days	1 year 11 months 23 days
Weighted average remaining vesting life, granted (in years)	1 year 11 months 1 day
Weighted average remaining vesting life, vested and expected to vest (in years)	1 year 10 months 13 days
Aggregate intrinsic value, unvested	$ 94,927	$ 50,431
Aggregate intrinsic value, vested and expected to vest	$ 94,927