Organization and Description of Business - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended
	Nov. 30, 2017	Oct. 31, 2017	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Net losses from operations since inception
Accumulated deficit				$ (109,211)	$ (101,550)
Stock transactions
Procceds from stock issuance, net of underwriting and offering costs				$ 64,500
Underwriter overallotment option
Stock transactions
Price (in dollars per share)	$ 17.00
Underwriter overallotment option | Common Stock [Member]
Stock transactions
Stock issued (in shares)	529,500
Follow-on public offering | Common Stock [Member]
Stock transactions
Stock issued (in shares)		3,530,000
Price (in dollars per share)		$ 17.00
Shelf offering
Stock transactions
Maximum aggregate offering price			$ 200,000
At-the-market offering
Stock transactions
Maximum aggregate offering price			$ 50,000