Summary of Significant Accounting Policies - Antidilutive shares excluded from earnings per share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securites excluded from computation of earnings per share (in shares)	10,076,405	8,081,596
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securites excluded from computation of earnings per share (in shares)	7,399,217	6,182,873
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securites excluded from computation of earnings per share (in shares)	2,677,188	1,866,831
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securites excluded from computation of earnings per share (in shares)	0	31,892