Stock-Based Compensation - Stock Option Activity (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Shares
Options outstanding at beginning of the period (in shares)	1,699,202
Granted (in shares)	1,512,675
Exercised (in shares)	(78,259)
Canceled (in shares)	(91,389)
Options outstanding at the end of the period (in shares)	3,042,229	1,699,202
Options vested and expected to vest at the end of the period (in shares)	2,881,532
Options exercisable at the end of the period (in shares)	907,982
Shares available for grant under the 2008 Plan	898,977
Weighted Average Exercise Price Per Share
Options outstanding at beginning of the period (in dollars per share)	$ 44.87
Granted (in dollars per share)	10.53
Exercised (in dollars per share)	4.57
Canceled (in dollars per share)	41.86
Options outstanding at the end of the period (in dollars per share)	28.93	$ 44.87
Options vested and expected to Vest at the end of the period (in dollars per share)	30.04
Options exercisable at the end of the period (in dollars per share)	$ 76.39
Weighted Average Remaining Contractual Term (In Years)
Options outstanding at the end of the period	0 years	8 years
Options vested and expected to vest at the end of the period	0 years
Options exercisable at the end of the period	0 years