CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		93,126,000
Beginning balance at Dec. 31, 2018	$ 121,763	$ 931	$ 586,940	$ 0	$ (466,108)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options (in shares)	4,205,000	4,205,000
Exercise of stock options	$ 19,048	$ 42	19,006
Vesting of restricted stock units (in shares)		479,000
Vesting of restricted stock units	0	$ 5	(5)
Issuance of common stock under employee stock purchase plan (in shares)		777,000
Issuance of common stock under employee stock purchase plan	15,129	$ 8	15,121
Stock-based compensation	41,928		41,928
Other comprehensive income (loss)	50			50
Net loss	(99,013)				(99,013)
Ending balance (in shares) at Dec. 31, 2019		98,587,000
Ending balance at Dec. 31, 2019	$ 98,905	$ 986	662,990	50	(565,121)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options (in shares)	2,956,000	2,956,000
Exercise of stock options	$ 21,709	$ 29	21,680
Vesting of restricted stock units (in shares)		1,504,000
Vesting of restricted stock units	0	$ 15	(15)
Issuance of common stock under employee stock purchase plan (in shares)		668,000
Issuance of common stock under employee stock purchase plan	13,040	$ 7	13,033
Stock-based compensation	59,782		59,782
Other comprehensive income (loss)	(40)			(40)
Net loss	$ (42,731)				(42,731)
Ending balance (in shares) at Dec. 31, 2020	103,715,000	103,715,000
Ending balance at Dec. 31, 2020	$ 150,665	$ 1,037	757,470	10	(607,852)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Exercise of stock options (in shares)	2,671,000	2,671,000
Exercise of stock options	$ 18,268	$ 26	18,242
Vesting of restricted stock units (in shares)		1,872,000
Vesting of restricted stock units	0	$ 19	(19)
Issuance of common stock under employee stock purchase plan (in shares)		671,000
Issuance of common stock under employee stock purchase plan	13,736	$ 7	13,729
Stock-based compensation	79,637		79,637
Other comprehensive income (loss)	(316)			(316)
Net loss	$ (46,677)				(46,677)
Ending balance (in shares) at Dec. 31, 2021	108,929,000	108,929,000
Ending balance at Dec. 31, 2021	$ 215,313	$ 1,089	$ 869,059	$ (306)	$ (654,529)