Summary of Significant Accounting Policies - Net Loss per Share (Details) - shares	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									7,852,873	3,732,643	2,846,668
Weighted-average number of common shares used in net loss per share applicable to common stockholders - basic and diluted	42,885,208	42,439,338	41,673,275	33,766,333	33,694,756	33,653,479	32,892,712	30,335,164	40,222,182	32,656,237	25,406,845
Stock options
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									4,618,421	3,732,643	2,846,668
Unvested Restricted Stock Unit
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									1,116,358
Warrants
Anti-dilutive securities
Total shares excluded from diluted net loss per share applicable to common stockholders									2,118,094