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The Company and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Feb. 12, 2018	Mar. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Sale of Stock
Issuance of stock (in shares)		3,592,858
Total stockholders’ (deficit) equity		$ 20,817	$ (1,025)	$ 1,964	$ 4,446	$ 7,774	$ 10,853	$ 15,048	$ 3,941
Accumulated deficit			(94,262)			(84,111)
Cash and cash equivalents			$ 1,855			$ 18,954	$ 23,806
Follow On Offering
Sale of Stock
Issuance of stock (in shares)	3,142,858
Share price (in dollars per share)	$ 7.00
Net proceeds	$ 23,100
Overallotment
Sale of Stock
Issuance of stock (in shares)	450,000