Stock Incentive Plans - Summary of Option Activity under Plans (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding at Beginning Balance | shares	4,843,018
Number of Options, Granted | shares	1,200,650
Number of Options, Exercised | shares	(41,593)
Number of Options, Cancelled/Forfeited | shares	(189,243)
Number of Options, Outstanding at Ending Balance | shares	5,812,832	4,843,018
Number of Options, Vested and Expected to vest at March 31, 2020 | shares	5,812,832
Number of Options, Exercisable at March 31, 2020 | shares	2,574,662
Weighted-Average Exercise Price per Share, Outstanding at Beginning Balance | $ / shares	$ 14.78
Weighted-Average Exercise Price per Share, Granted | $ / shares	18.43
Weighted-Average Exercise Price per Share, Exercised | $ / shares	3.84
Weighted-Average Exercise Price per Share, Cancelled/Forfeited | $ / shares	23.31
Weighted-Average Exercise Price per Share, Outstanding at Ending Balance | $ / shares	15.33	$ 14.78
Weighted-Average Exercise Price per Share, Vested and Expected to vest at March 31, 2020 | $ / shares	15.33
Weighted-Average Exercise Price Per Share, Exercisable at March 31, 2020 | $ / shares	$ 11.70
Weighted Average Remaining Contractual Term, Outstanding	8 years 1 month 6 days	8 years 6 months
Weighted Average Remaining Contractual Term, Vested and Expected to vest at March 31, 2020	8 years 1 month 6 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2020	7 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance | $	$ 11,299	$ 33,809
Aggregate Intrinsic Value, Vested and Expected to vest at March 31, 2020 | $	11,299
Aggregate Intrinsic Value, Exercisable at March 31, 2020 | $	$ 9,618