Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional paid in capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2019	$ 450,197	$ 4	$ 627,810	$ 205	$ (177,822)
Balances (Shares) at Dec. 31, 2019		36,992
Exercise of stock options	4,247		4,247
Exercise of stock options, Shares		356
Issuance of common stock under employee stock purchase plan	1,799		1,799
Issuance of common stock under employee stock purchase plan, shares		55
Stock-based compensation expense	24,368		24,368
Unrealized gain(loss) on available-for-sale securities, net	58			58
Net income (loss)	(65,009)				(65,009)
Balances at Sep. 30, 2020	415,660	$ 4	658,224	263	(242,831)
Balances (Shares) at Sep. 30, 2020		37,404
Balances at Jun. 30, 2020	397,861	$ 4	648,729	750	(251,622)
Balances (Shares) at Jun. 30, 2020		37,291
Exercise of stock options	268		268
Exercise of stock options, Shares		74
Issuance of common stock under employee stock purchase plan	1,192		1,192
Issuance of common stock under employee stock purchase plan, shares		38
Stock-based compensation expense	8,035		8,035
Unrealized gain(loss) on available-for-sale securities, net	(487)			(487)
Net income (loss)	8,791				8,791
Balances at Sep. 30, 2020	415,660	$ 4	658,224	263	(242,831)
Balances (Shares) at Sep. 30, 2020		37,404
Balances at Dec. 31, 2020	377,753	$ 4	667,181	(360)	(289,072)
Balances (Shares) at Dec. 31, 2020		37,476
Issuance of common stock upon public offering, net of transaction costs	216,059		216,059
Issuance of stock, net of transaction costs		4,899
Exercise of stock options	3,296		3,296
Exercise of stock options, Shares		324
Issuance of common stock under employee stock purchase plan	1,768		1,768
Issuance of common stock under employee stock purchase plan, shares		54
Stock-based compensation expense	29,646		29,646
Unrealized gain(loss) on available-for-sale securities, net	(925)			(925)
Net income (loss)	(166,183)				(166,183)
Balances at Sep. 30, 2021	461,414	$ 4	917,950	(1,285)	(455,255)
Balances (Shares) at Sep. 30, 2021		42,752
Balances at Jun. 30, 2021	507,245	$ 4	905,346	(1,255)	(396,850)
Balances (Shares) at Jun. 30, 2021		42,555
Exercise of stock options	1,729		1,729
Exercise of stock options, Shares		163
Issuance of common stock under employee stock purchase plan	1,141		1,141
Issuance of common stock under employee stock purchase plan, shares		35
Stock-based compensation expense	9,734		9,734
Unrealized gain(loss) on available-for-sale securities, net	(30)			(30)
Net income (loss)	(58,405)				(58,405)
Balances at Sep. 30, 2021	$ 461,414	$ 4	$ 917,950	$ (1,285)	$ (455,255)
Balances (Shares) at Sep. 30, 2021		42,752