CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (unaudited) - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2019	$ 301,984		$ 1	$ 705,143	$ (444)	$ (402,716)
Beginning balance, Shares at Dec. 31, 2019			136,054,000
Common stock issued upon vesting of restricted stock units	0		$ 0	0	0	0
Common stock issued upon vesting of restricted stock units, Shares			945,000
Common stock issued upon stock option exercise	13,815		$ 0	13,815	0	0
Common stock issued upon stock option exercise, Shares			1,071,000
Stock-based compensation expense	18,278		$ 0	18,278	0	0
Comprehensive loss	(2,436)	[1]	0	0	(2,436)	0
Net loss	(24,250)		0	0	0	(24,250)
Ending balance at Mar. 31, 2020	307,391		$ 1	737,236	(2,880)	(426,966)
Ending balance, Shares at Mar. 31, 2020			138,070,000
Beginning Balance at Dec. 31, 2020	346,356		$ 1	835,444	5,208	(494,297)
Beginning balance, Shares at Dec. 31, 2020			143,820,000
Common stock issued upon vesting of restricted stock units	0		$ 0	0	0	0
Common stock issued upon vesting of restricted stock units, Shares			967,000
Common stock issued upon stock option exercise	$ 9,572		$ 0	9,572	0	0
Common stock issued upon stock option exercise, Shares	641,252		641,000
Issuance of restricted stock awards	$ 0		$ 0	0	0	0
Issuance of restricted stock awards, Shares			274,000
Cancellation of restricted stock awards	0		$ 0	0	0	0
Cancellation of restricted stock awards, Shares			(64,000)
Stock-based compensation expense	24,158		$ 0	24,158	0	0
Comprehensive loss	(2,953)	[1]	0	0	(2,953)	0
Net loss	(29,647)		0	0	0	(29,647)
Ending balance at Mar. 31, 2021	$ 347,486		$ 1	$ 869,174	$ 2,255	$ (523,944)
Ending balance, Shares at Mar. 31, 2021			145,638,000

[1] Net of tax effect which was not material.