CONSOLIDATED SUPPLEMENTARY FINANCIAL DATA (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Revenue	$ 61,913	$ 56,915	$ 59,930	$ 63,989	$ 59,947	$ 57,399	$ 58,297	$ 48,384	$ 242,747	$ 224,027	$ 231,201
Cost of revenue
Cost of revenue	13,451	15,264	16,148	15,885	14,576	12,574	13,027	11,198	60,748	51,375	53,701
Gross Profit	48,462	41,651	43,782	48,104	45,371	44,825	45,270	37,186	181,999	172,652	177,500
Operating expenses
Operating Expenses	59,466	54,151	56,246	58,943	58,582	67,698	82,316	68,595	228,806	277,191	264,467
Operating loss	(11,004)	(12,500)	(12,464)	(10,839)	(13,211)	(22,873)	(37,046)	(31,409)	(46,807)	(104,539)	(86,967)
Net loss	$ (12,066)	$ (12,779)	$ (10,781)	$ (7,983)	$ (9,532)	$ (17,331)	$ (36,980)	$ (26,576)	$ (43,609)	$ (90,419)	$ (157,957)
Net loss per share:
Basic (in dollars per share)	$ (0.11)	$ (0.11)	$ (0.09)	$ (0.07)	$ (0.09)	$ (0.16)	$ (0.33)	$ (0.24)	$ (0.39)	$ (0.81)	$ (1.46)
Diluted (in dollars per share)	$ (0.11)	$ (0.11)	$ (0.09)	$ (0.07)	$ (0.09)	$ (0.16)	$ (0.33)	$ (0.24)	$ (0.39)	$ (0.81)	$ (1.46)
Shares used in per share calculations:
Basic (in shares)	112,706	113,828	113,572	112,907	111,883	111,315	110,875	109,692	113,254	110,948	108,450
Diluted (in shares)	112,706	113,828	113,572	112,907	111,883	111,315	110,875	109,692	113,254	110,948	108,450