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Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 21, 2018	Aug. 06, 2018	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Stock transactions
Net proceeds from sale of stock						$ 34,492	$ 1,025
Par value (per share)				$ 0.00001		$ 0.00001		$ 0.00001
Common Stock
Stock transactions
Common stock sold pursuant to Sales Agreement (in shares)				1,924,957	103,500	2,846,641	103,500
Common stock issued pursuant to exercise of Exchange Warrants (in shares)						599,997
Common Stock \| Shelf offering
Stock transactions
Maximum aggregate offering price			$ 200,000
Common Stock \| Private Placement
Stock transactions
Number of warrants exercised				0		0
Cantor Fitzgerald & Co. Sales Agreement
Stock transactions
Common stock available for sale				$ 72,000		$ 72,000
Cantor Fitzgerald & Co. Sales Agreement \| At-the-market offering
Stock transactions
Maximum aggregate offering price			$ 50,000
Common stock available for sale				$ 13,000		$ 13,000
Cantor Fitzgerald & Co. Sales Agreement \| Common Stock \| At-the-market offering
Stock transactions
Common stock sold pursuant to Sales Agreement (in shares)				1,924,957	103,500	2,846,641	103,500
Net proceeds from sale of stock				$ 23,900	$ 1,000	$ 34,500	$ 1,000
Investors \| Common Stock
Stock transactions
Common stock sold pursuant to Sales Agreement (in shares)		2,750,000
Price (in dollars per share)		$ 8.00
Aggregate gross proceeds		$ 21,700
Investors \| Common Stock \| Private Placement
Stock transactions
Warrants to purchase common stock, number of shares		2,750,000
Purchase of common stock		2,750,000
Exchange Agreement \| Exchanging Stockholders
Stock transactions
Warrants to purchase common stock, number of shares	1,000,000
Warrants exercise price	$ 0.00001
Common stock exchanged for pre-funded warrants	1,000,000
Par value (per share)	$ 0.00001
Purchase of common stock	1,000,000
Exercise Price (per share)	$ 0.00001
Duration of warrants from date of issuance (in years)	10 years
Equity Method Investment, Ownership Percentage	9.99%
Exchange Agreement \| Exchanging Stockholders \| Common Stock
Stock transactions
Number of warrants exercised				600,000		600,000
Common stock issued pursuant to exercise of Exchange Warrants (in shares)						599,997
Exchange Warrants unexercised				400,000		400,000
Group one \| Common Stock \| Private Placement
Stock transactions
Number of shares to be converted for each warrant		1,375,000
Warrants exercise price		$ 10.00
Exercise Price (per share)		$ 10.00
Group two \| Common Stock \| Private Placement
Stock transactions
Number of shares to be converted for each warrant		1,375,000
Warrants exercise price		$ 15.00
Exercise Price (per share)		$ 15.00