Stockholders' Equity - Summary of Option Activity under 2013 Plan and 2010 Plan (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Options
Number of Shares, Options outstanding at beginning of period	781,725
Number of Shares, Options Granted	1,063,150
Number of Shares, Options Exercised	(7,813)
Number of Shares, Options Cancelled/forfeited	(451,398)
Number of Shares, Options outstanding at end of period	1,385,664	781,725
Number of Shares, Options exercisable at end of period	328,707
Weighted Average Exercise Price, Options
Weighted Average Exercise Price, Options outstanding at beginning of period	$ 16.34
Weighted Average Exercise Price, Options Granted	13.84
Weighted Average Exercise Price, Options Exercised	11.81
Weighted Average Exercise Price, Options Cancelled/forfeited	22.95
Weighted Average Exercise Price, Options outstanding at end of period	12.12	$ 16.34
Weighted Average Exercise Price, Options exercisable at end of period	$ 11.34
Weighted Average Remaining Contract Term, Options
Weighted Average Remaining Contractual Term, Options outstanding at beginning of period	8 years 10 months 24 days	9 years
Weighted Average Remaining Contractual Term, Options exercisable at end of period	7 years 2 months 12 days
Aggregate Intrinsic Value, Options outstanding at end of period	$ 0.1
Aggregate Intrinsic Value, Options exercisable at end of period	$ 0.1