Stockholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	9 Months Ended
	Mar. 04, 2019	Nov. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Class of Stock
Stock issued (in shares)			785,848
Net proceeds from offering of common stock			$ 2.3
Common stock, par value			$ 0.001	$ 0.001
"At-The-Market" Equity Program
Class of Stock
Stock issued (in shares)			532,700
Net proceeds from offering of common stock			$ 1.6
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement		3.00%
Lincoln Park Capital Fund, LLC (“Investor”)
Class of Stock
Value of shares investor has committed to purchase from time to time at Company’s sole discretion	$ 35.0
Stock issued (in shares)	269,749
Stock issued (per share)	$ 2.84
Common Stock | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock		$ 50.0