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, 2018	$ 508,848	$ 4	$ 592,580	$ (720)	$ (83,016)
Balances (Shares) at Dec. 31, 2018		36,120
Adoption of ASU 2016-02 (Topic 842) | ASU 2016-02 [Member]	(33)				(33)
Adoption of ASU 2016-02 (Topic 842) | ASU 2018-02 [Member]				40	(40)
Vesting of restricted stock units, Shares		40
Exercise of stock options	7,062		7,062
Exercise of stock options, Shares		796
Issuance of common stock under employee stock purchase plan	1,314		1,314
Issuance of common stock under employee stock purchase plan, shares		36
Stock-based compensation expense	26,854		26,854
Unrealized gain (loss) on available-for-sale securities, net	885			885
Net income (loss)	(94,733)				(94,733)
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	5,623		5,623
Exercise of stock options, Shares		428
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	31,949		31,949
Unrealized gain (loss) on available-for-sale securities, net	(565)			(565)
Net income (loss)	(111,250)				(111,250)
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	4,279		4,279
Exercise of stock options, Shares		403
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	38,808		38,808
Unrealized gain (loss) on available-for-sale securities, net	(2,209)			(2,209)
Net income (loss)	127,840				127,840
Balances at Dec. 31, 2021	$ 764,298	$ 4	$ 928,095	$ (2,569)	$ (161,232)
Balances (Shares) at Dec. 31, 2021		42,831