Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	12,313,878	14,032,786	12,810,852	13,404,840
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	2,487,135	2,215,086	2,398,467	1,835,879
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	9,826,743	11,817,700	10,412,385	11,568,961