Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Initial Public Offering	Initial Public Offering Convertible Notes	Common Stock	Common Stock Initial Public Offering	Common Stock Initial Public Offering Convertible Notes	Additional Paid-in Capital	Additional Paid-in Capital Initial Public Offering	Additional Paid-in Capital Initial Public Offering Convertible Notes	Accumulated Deficit	Series A Convertible Preferred Stock	Series A Convertible Preferred Stock Initial Public Offering	Series B Convertible Preferred Stock	Series B Convertible Preferred Stock Initial Public Offering	Series B-1 Convertible Preferred Stock	Series B-1 Convertible Preferred Stock Initial Public Offering	Series C Convertible Preferred Stock	Series C Convertible Preferred Stock Initial Public Offering	Series D Convertible Preferred Stock	Series D Convertible Preferred Stock Initial Public Offering	Series D-1 Convertible Preferred Stock	Series D-1 Convertible Preferred Stock Initial Public Offering
Beginning Balance at Dec. 31, 2016	$ (27,258,972)			$ 7			$ 3,641,693			$ (30,900,672)
Convertible Preferred Stock (Shares), Beginning Balance at Dec. 31, 2016											345,587		8,058,170		3,437,950		23,357,047		20,652,486		29,166,671
Convertible Preferred Stock, Beginning Balance at Dec. 31, 2016											$ 61,847		$ 842,845		$ 359,593		$ 5,547,841		$ 4,838,379		$ 13,766,022
Beginning Balance, Shares at Dec. 31, 2016				70,178
Issuance of convertible preferred stock																					$ 17,593,610
Issuance of convertible preferred stock, Shares																					36,974,586
Stock option exercises	14,295			$ 1			14,294
Stock option exercises, Shares				7,079
Stock-based compensation expense	382,830						382,830
Net loss	(23,365,364)									(23,365,364)
Ending Balance at Dec. 31, 2017	(50,227,211)			$ 8			4,038,817			(54,266,036)
Convertible Preferred Stock (Shares), Ending Balance at Dec. 31, 2017											345,587		8,058,170		3,437,950		23,357,047		20,652,486		66,141,257
Convertible Preferred Stock, Ending Balance at Dec. 31, 2017											$ 61,847		$ 842,845		$ 359,593		$ 5,547,841		$ 4,838,379		$ 31,359,632
Ending Balance, Shares at Dec. 31, 2017				77,257
Stock option exercises	3,499						3,499
Stock option exercises, Shares				1,856
IPO Units		$ 19,389,978			$ 386			$ 19,389,592
IPO Units, Shares					3,864,000
Conversion of preferred stock and convertible debt		$ 43,010,137	$ 14,898,327		$ 285	$ 323		$ 43,009,852	$ 14,898,004			$ (61,847)		$ (842,845)		$ (359,593)		$ (5,547,841)		$ (4,838,379)		$ (31,359,632)
Conversion of preferred stock and convertible debt Shares					2,850,280	3,239,294						(345,587)		(8,058,170)		(3,437,950)		(23,357,047)		(20,652,486)		(66,141,257)
Conversion of preferred stock warrants into common stock warrants	84,676						84,676
Stock-based compensation expense	160,551						160,551
Net loss	(12,084,936)									(12,084,936)
Ending Balance at Sep. 30, 2018	$ 15,235,022			$ 1,002			$ 81,584,992			$ (66,350,972)
Convertible Preferred Stock (Shares), Ending Balance at Sep. 30, 2018											0		0		0		0		0		0
Ending Balance, Shares at Sep. 30, 2018				10,032,687