Stock-Based Compensation - Stock Option Activity (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Shares
Options Outstanding at beginning of the period (in shares)	866,132
Granted (in shares)	940,040
Canceled (in shares)	(106,970)
Options Outstanding at the end of the period (in shares)	1,699,202	866,132
Options Vested and Expected to Vest at the end of the period (in shares)	1,580,780
Options Exercisable at the end of the period (in shares)	573,996
Shares Available for Grant Under the 2008 Plan	424,263
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 93.70
Granted (in dollars per share)	2.77
Canceled (in dollars per share)	70.22
Options Outstanding at the end of the period (in dollars per share)	44.87	$ 93.70
Options Vested and Expected to Vest at the end of the period (in dollars per share)	47.90
Options Exercisable at the end of the period (in dollars per share)	$ 121.76
Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at the end of the period	8 years	7 years 1 month 6 days
Options Vested and Expected to Vest at the end of the period	7 years 10 months 24 days
Options Exercisable at the end of the period	5 years 6 months