Share-Based Compensation - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		93 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Oct. 31, 2019
Stock options
Stock Option and Compensation Plans
Unrecognized share-based compensation costs for option awards, net of estimated forfeitures		$ 7,200		$ 7,200		$ 7,200
Expected weighted average period to recognize share-based compensation costs (in years)				2 years 8 months 12 days
Restricted stock units
Stock Option and Compensation Plans
Expected weighted average period to recognize share-based compensation costs (in years)				2 years 7 months 6 days
Unrecognized compensation costs, net of estimated forfeitures		$ 4,200		$ 4,200		$ 4,200
Employee stock purchase plan
Stock Option and Compensation Plans
Common stock issued (in shares)		32,821	38,944	76,402	70,466
Proceeds from stock plans				$ 147	$ 81
2013 Plan
Stock Option and Compensation Plans
Increase in number of shares available under the Plan (in shares)				1,985,000		10,539,000
Annual increase in shares reserved for issuance under the Plan (as a percent)				4.00%
Number of shares of common stock available for issuance under the Plan (in shares)		2,666,000		2,666,000		2,666,000
2013 Plan | Employee stock purchase plan
Stock Option and Compensation Plans
Number of shares available for future purchase (in shares)		805,361		805,361		805,361
2019 Inducement Plan | Stock options
Stock Option and Compensation Plans
Increase in number of shares available under the Plan (in shares)	1,000,000
Number of shares of common stock available for issuance under the Plan (in shares)		610,000		610,000		610,000
Number of initial shares reserved for issuance under the Plan (in shares)							1,000,000