Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended
	Jan. 31, 2012	Oct. 31, 2011	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Apr. 30, 2011
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			225,000,000		225,000,000
Preferred stock, par value (in dollars per share)			$ 0.001		$ 0.001
Change in fair value of redeemable convertible preferred stock warrant liability			$ 1,200	$ 0	$ 1,517
Class B common stock
Class of Stock [Line Items]
Number of shares issued from exercise of warrants (in shares)						174,347
Warrant To Purchase Series B Redeemable Preferred Stock
Class of Stock [Line Items]
Number of shares subject to purchase from warrant (in shares)	23,760	94,510					59,140
Proceeds from drawdown	$ 400	$ 1,600
Exercise price of warrants (in dollars per share)							$ 0.34