Significant Accounting Policies - Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the computation of diluted net loss per share (in shares)	9,761,700	9,413,016	9,761,700	9,413,016
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the computation of diluted net loss per share (in shares)	8,790,185	8,535,266	8,790,185	8,535,266
Stock purchase warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the computation of diluted net loss per share (in shares)	0	79,500	0	79,500
Non-vested restricted stock awards and performance share units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the computation of diluted net loss per share (in shares)	858,147	755,179	858,147	755,179
Non-vested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common stock equivalents excluded from the computation of diluted net loss per share (in shares)	113,368	43,071	113,368	43,071