Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Per Share
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	2,751,751	14,607,106	11,259,726
Convertible preferred stock outstanding (in shares)
Loss Per Share
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	0	12,111,706	9,367,628
Convertible preferred stock warrants (in shares)
Loss Per Share
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	0	423,784	394,587
Convertible common stock warrants (in shares)
Loss Per Share
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	6,595	0	0
Common stock options outstanding (in shares)
Loss Per Share
Antidilutive securities excluded from computation of diluted weighted average shares outstanding (in shares)	2,745,156	2,071,616	1,497,511