Stockholders' Equity - Common Stock (Details) $ / shares in Units, $ in Millions					1 Months Ended	12 Months Ended
	Mar. 04, 2019 USD ($) $ / shares shares	Nov. 01, 2017 USD ($) shares	Oct. 30, 2017 USD ($) person $ / shares shares	May 05, 1998 $ / shares shares	Nov. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / shares shares
Class of Stock
Stock issued (in shares)						1,535,848
Net proceeds from offering of common stock | $						$ 3.7
Common stock, shares reserved for future issuance						25,066,074
Common stock, par value | $ / shares						$ 0.001	$ 0.001
"At-The-Market" Equity Program
Class of Stock
Stock issued (in shares)						532,700	0
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement					3.00%
Gross proceeds from offering of common stock | $						$ 1.6
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) | $ / shares	$ 2.84
Common Stock
Class of Stock
Stock issued (in shares)		625,000	4,166,666	149,960
Sale price of common shares subject to the liquidation put | $ / shares				$ 128.00
Minimum closing sales price of common stock to issue termination notice to put holders | $ / shares						$ 256.00
Price exceeds on number of days						20 days
Liquidation put shares no longer held by original holders						49,993
Shares held by put holders						4,472
Put Rights outstanding						0
Remaining shares of common stock subject to the liquidation put						95,494
Net proceeds from offering of common stock | $		$ 53.7
Number of days underwriters have to purchase additional shares		30 days
Stock price (in dollars per share) | $ / shares			$ 12.00
Gross proceeds from offering of common stock | $			$ 50.0
Common Stock | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock | $					$ 50.0
Baker Bros. Advisors LP | Common Stock
Class of Stock
Stock issued (in shares)			1,000,000
Number of people | person			2