Condensed Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2019	$ (372,187)		$ 1	$ 357	$ 22	$ (372,567)
Temporary Equity, Beginning Balance (shares) at Dec. 31, 2019		147,214
Temporary Equity, Beginning Balance at Dec. 31, 2019		$ 409,446
Beginning Balance (shares) at Dec. 31, 2019			922
Temporary Equity, Issuance of Series E redeemable convertible preferred stock, net of issuance costs		$ 126,758
Temporary Equity, Issuance of Series E redeemable convertible preferred stock, net of issuance costs (shares)		57,782
Issuance of common stock on settlement of accrued dividend	41,763		$ 5	41,758
Temporary Equity, Issuance of common stock on settlement of accrued dividend		$ (41,763)
Issuance of common stock on settlement of accrued dividend (shares)			4,850
Deemed dividend on settlement of accrued dividend	42,530			42,530
Temporary Equity, Deemed dividend on settlement of accrued dividend		(42,530)
Stock option exercises	14			14
Stock option exercises (shares)			4
Stock-based compensation expense	580			580
Unrealized loss on available-for-sale securities	(35)				(35)
Adjustment to redemption value on redeemable convertible preferred stock	(362)			(362)
Temporary equity, Adjustment to redemption value on redeemable convertible preferred stock		$ 362
Net loss	(20,650)					(20,650)
Ending Balance at Mar. 31, 2020	(308,347)		$ 6	84,877	(13)	(393,217)
Temporary Equity, Ending Balance (shares) at Mar. 31, 2020		204,996
Temporary Equity, Ending Balance at Mar. 31, 2020		$ 452,273
Ending Balance (shares) at Mar. 31, 2020			5,776
Beginning Balance at Dec. 31, 2020	328,609		$ 43	822,624	1	(494,059)
Beginning Balance (shares) at Dec. 31, 2020			42,722
Issuance of common stock through employee stock purchase plan	1,838			1,838
Issuance of common stock through employee stock purchase plan (shares)			80
Stock option exercises	380			380
Stock option exercises (shares)			86
Stock-based compensation expense	5,852			5,852
Unrealized loss on available-for-sale securities	(9)				(9)
Net loss	(30,025)					(30,025)
Ending Balance at Mar. 31, 2021	$ 306,645		$ 43	$ 830,694	$ (8)	$ (524,084)
Ending Balance (shares) at Mar. 31, 2021			42,888