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Exercise price per share or per unit of warrants or rights outstanding.

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Organization and Description of Business - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended		3 Months Ended	9 Months Ended
	Aug. 06, 2018	Nov. 30, 2017	Oct. 31, 2017	Nov. 30, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Net losses from operations since inception
Accumulated deficit						$ (126,609)	$ (126,609)	$ (101,550)
Stock transactions
Common stock sold						24,138,102	24,138,102	21,088,306
Net proceeds from sale of stock							$ 1,025
Common Stock
Stock transactions
Stock issued (in shares)			3,530,000
Price (in dollars per share)			$ 17.00
Procceds from stock issuance, net of underwriting and offering costs				$ 64,500
Underwriter overallotment option \| Common Stock
Stock transactions
Stock issued (in shares)		529,500
Price (in dollars per share)		$ 17.00		$ 17.00
Shelf offering \| Common Stock
Stock transactions
Maximum aggregate offering price					$ 200,000
Private Placement \| Common Stock
Stock transactions
Number of warrants exercised						0	0
Cantor Fitzgerald & Co. Sales Agreement \| At-the-market offering
Stock transactions
Maximum aggregate offering price					$ 50,000
Gross proceeds for any common stock sold, maximum percent payable							3.00%
Common stock sold						103,500	103,500
Net proceeds from sale of stock						$ 1,100	$ 1,100
Common stock available for sale						$ 48,800	$ 48,800
Investors \| Common Stock
Stock transactions
Stock issued (in shares)	2,750,000
Price (in dollars per share)	$ 8.00
Aggregate gross proceeds	$ 22,000
Investors \| Private Placement \| Common Stock
Stock transactions
Warrants to purchase common stock, number of shares	2,750,000
Group one \| Private Placement \| Common Stock
Stock transactions
Number of shares to be converted for each warrant	1,375,000
Warrants exercise price	$ 10.00
Group two \| Private Placement \| Common Stock
Stock transactions
Number of shares to be converted for each warrant	1,375,000
Warrants exercise price	$ 15.00