Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2016	$ (177,124)		$ 2	$ 3,761	$ (180,887)
Beginning balance, shares at Dec. 31, 2016		264,374
Beginning balance at Dec. 31, 2016		$ 172,311
Beginning balance, shares at Dec. 31, 2016			187
Issuance of Series G convertible preferred stock, net of issuance costs of $175		$ 14,825
Issuance of restricted stock awards, shares			11
Share-based awards and options exercises	35			35
Share-based awards and options exercises, shares			33
Share-based compensation expense	496			496
Net loss	(16,059)				(16,059)
Ending balance at Dec. 31, 2017	(192,652)		$ 2	4,292	(196,946)
Ending balance, shares at Dec. 31, 2017		304,958
Ending balance at Dec. 31, 2017		$ 187,136
Ending balance, shares at Dec. 31, 2017			231
Issuance Of Series G Convertible Preferred Stock Issuance Cost, shares		40,584
Conversion of convertible preferred stock into common stock	187,136	$ (187,136)	$ 109	187,027
Conversion of convertible preferred stock into common stock, shares		(304,958)	10,994
Conversion of convertible preferred stock warrants into common stock warrants	1,874			1,874
Issuance of common stock in initial public offering, net of issuance costs of $3,463	96,535		$ 64	96,471
Issuance of common stock in initial public offering, net of issuance costs of $3.464, shares			6,325
Share-based awards and options exercises	503		$ 2	501
Share-based awards and options exercises, shares			194
Share-based compensation expense	1,743			1,743
Net loss	(24,097)				(24,097)
Ending balance at Dec. 31, 2018	71,042		$ 177	291,908	(221,043)
Ending balance, shares at Dec. 31, 2018			17,744
Share-based awards and options exercises	2,420		$ 9	2,411
Share-based awards and options exercises, shares			901
Share-based compensation expense	3,434			3,434
Net loss	(29,044)				(29,044)
Ending balance at Dec. 31, 2019	$ 47,852		$ 186	$ 297,753	$ (250,087)
Ending balance, shares at Dec. 31, 2019			18,645