Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (unaudited) - USD ($) $ in Thousands	Total	IPO	Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock IPO	Common Stock	Common Stock IPO	Additional Paid-in Capital	Accumulated Deficit	Non-controlling Interest
Beginning balance at Dec. 31, 2017	$ (98,578)				$ 1		$ 2,977	$ (101,556)	$ 0
Beginning balance (in shares) at Dec. 31, 2017					663,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	284						284
Exercise of stock options (in shares)					186,944
Employee stock-based compensation	164						164
Nonemployee stock-based compensation	(2)						(2)
Net loss	(5,408)							(5,408)
Comprehensive loss	(5,408)							(5,408)
Ending balance at Mar. 31, 2018	(103,453)				$ 1		3,436	(106,890)	0
Ending balance (in shares) at Mar. 31, 2018					850,214
Temporary equity, beginning balance at Dec. 31, 2017			$ 105,235
Temporary equity, beginning balance (in shares) at Dec. 31, 2017			21,233,190
Temporary equity, ending balance at Mar. 31, 2018			$ 105,235
Temporary equity, ending balance (in shares) at Mar. 31, 2018			21,233,190
Beginning balance at Dec. 31, 2017	(98,578)				$ 1		2,977	(101,556)	0
Beginning balance (in shares) at Dec. 31, 2017					663,270
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(22,011)
Comprehensive loss	(22,011)
Ending balance at Sep. 30, 2018	(119,169)				$ 1		4,323	(123,493)	0
Ending balance (in shares) at Sep. 30, 2018					1,097,838
Temporary equity, beginning balance at Dec. 31, 2017			$ 105,235
Temporary equity, beginning balance (in shares) at Dec. 31, 2017			21,233,190
Temporary equity, ending balance at Sep. 30, 2018			$ 105,235
Temporary equity, ending balance (in shares) at Sep. 30, 2018			21,233,190
Beginning balance at Mar. 31, 2018	(103,453)				$ 1		3,436	(106,890)	0
Beginning balance (in shares) at Mar. 31, 2018					850,214
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	148						148
Exercise of stock options (in shares)					106,732
Employee stock-based compensation	178						178
Nonemployee stock-based compensation	151						151
Net loss	(7,651)							(7,651)
Comprehensive loss	(7,651)							(7,651)
Ending balance at Jun. 30, 2018	(110,627)				$ 1		3,913	(114,541)	0
Ending balance (in shares) at Jun. 30, 2018					956,946
Temporary equity, beginning balance at Mar. 31, 2018			$ 105,235
Temporary equity, beginning balance (in shares) at Mar. 31, 2018			21,233,190
Temporary equity, ending balance at Jun. 30, 2018			$ 105,235
Temporary equity, ending balance (in shares) at Jun. 30, 2018			21,233,190
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	216						216
Exercise of stock options (in shares)					140,892
NeuroCo common stock issuance	1								1
Employee stock-based compensation	179						179
Nonemployee stock-based compensation	15						15
Net loss	(8,953)							(8,952)	(1)
Comprehensive loss	(8,953)							(8,952)	(1)
Ending balance at Sep. 30, 2018	(119,169)				$ 1		4,323	(123,493)	$ 0
Ending balance (in shares) at Sep. 30, 2018					1,097,838
Temporary equity, ending balance at Sep. 30, 2018			$ 105,235
Temporary equity, ending balance (in shares) at Sep. 30, 2018			21,233,190
Beginning balance at Dec. 31, 2018	(134,553)				$ 1		4,557	(139,111)
Beginning balance (in shares) at Dec. 31, 2018					1,135,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	375						375
Exercise of stock options (in shares)					251,305
Employee stock-based compensation	241						241
Nonemployee stock-based compensation	21						21
Net loss	(24,158)							(24,158)
Comprehensive loss	(24,158)							(24,158)
Ending balance at Mar. 31, 2019	(158,074)				$ 1		5,194	(163,269)
Ending balance (in shares) at Mar. 31, 2019					1,386,615
Temporary equity, beginning balance at Dec. 31, 2018	$ 105,235		$ 105,235
Temporary equity, beginning balance (in shares) at Dec. 31, 2018	21,233,190		21,233,190
Increase (Decrease) in Temporary Equity [Roll Forward]
Exercise of warrants	$ 0		$ 30
Exercise of warrants (in shares)			4,915
Temporary equity, ending balance at Mar. 31, 2019			$ 105,265
Temporary equity, ending balance (in shares) at Mar. 31, 2019			21,238,105
Beginning balance at Dec. 31, 2018	$ (134,553)				$ 1		4,557	(139,111)
Beginning balance (in shares) at Dec. 31, 2018					1,135,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	456,147
Net loss	$ (44,124)
Comprehensive loss	(44,124)
Ending balance at Sep. 30, 2019	77,443				$ 31		260,647	(183,235)
Ending balance (in shares) at Sep. 30, 2019					30,775,980
Temporary equity, beginning balance at Dec. 31, 2018	$ 105,235		$ 105,235
Temporary equity, beginning balance (in shares) at Dec. 31, 2018	21,233,190		21,233,190
Temporary equity, ending balance at Sep. 30, 2019	$ 0		$ 0
Temporary equity, ending balance (in shares) at Sep. 30, 2019	0		0
Beginning balance at Mar. 31, 2019	$ (158,074)				$ 1		5,194	(163,269)
Beginning balance (in shares) at Mar. 31, 2019					1,386,615
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	364				$ 1		363
Exercise of stock options (in shares)					176,576
Issuance of common stock in connection with IPO, net of underwriting discount, commissions and offering costs of $2,561	109,039				$ 6		109,033
Issuance of common stock in connection with IPO, net of underwriting discount, commissions and offering costs (in shares)					6,000,000
Employee stock-based compensation	814						814
Nonemployee stock-based compensation	22						22
Net loss	(11,959)							(11,959)
Comprehensive loss	(11,959)							(11,959)
Ending balance at Jun. 30, 2019	84,377				$ 31		259,574	(175,228)
Ending balance (in shares) at Jun. 30, 2019					30,747,714
Temporary equity, beginning balance at Mar. 31, 2019			$ 105,265
Temporary equity, beginning balance (in shares) at Mar. 31, 2019			21,238,105
Increase (Decrease) in Temporary Equity [Roll Forward]
Exercise of warrants	31	$ 0	$ 1,754	$ 37,121			31
Exercise of warrants (in shares)			287,446	1,653,004	3,764	2,204
Conversion of preferred stock to common stock upon IPO	144,140		$ (144,140)		$ 23		144,117
Conversion of preferred stock to common stock upon IPO (in shares)			(23,178,555)		23,178,555
Temporary equity, ending balance at Jun. 30, 2019			$ 0
Temporary equity, ending balance (in shares) at Jun. 30, 2019			0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	68						68
Exercise of stock options (in shares)					28,266
Decrease in IPO offering costs	80						80
Employee stock-based compensation	902						902
Nonemployee stock-based compensation	23						23
Net loss	(8,007)							(8,007)
Comprehensive loss	(8,007)							(8,007)
Ending balance at Sep. 30, 2019	77,443				$ 31		$ 260,647	$ (183,235)
Ending balance (in shares) at Sep. 30, 2019					30,775,980
Temporary equity, ending balance at Sep. 30, 2019	$ 0		$ 0
Temporary equity, ending balance (in shares) at Sep. 30, 2019	0		0