CONSOLIDATED SUPPLEMENTARY FINANCIAL DATA (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								6 Months Ended	9 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	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue
Revenue	$ 61,913	$ 56,915	$ 61,717	$ 65,777	$ 61,735	$ 59,187	$ 58,297	$ 48,384	$ 127,494	$ 184,409	$ 165,868		$ 246,322	$ 227,603	$ 231,201
Cost of revenue
Cost of revenue	13,451	15,264	16,148	15,885	14,576	12,574	13,027	11,198	32,033	47,297	36,799		60,748	51,375	53,701
Gross Profit	48,462	41,651	45,569	49,892	47,159	46,613	45,270	37,186	95,461	137,112	129,069		185,574	176,228	177,500
Operating expenses
Total operating expenses	59,466	54,151	56,657	59,354	57,760	67,698	82,316	68,595	116,011	170,162	218,609		229,628	276,369	264,467
Operating loss	(11,004)	(12,500)	(11,088)	(9,462)	(10,601)	(21,085)	(37,046)	(31,409)	(20,550)	(33,050)	(89,540)		(44,054)	(100,141)	(86,967)
Net loss	$ (12,055)	$ (12,737)	$ (9,140)	$ (6,539)	$ (6,876)	$ (15,532)	$ (36,980)	$ (26,576)	$ (15,679)	$ (28,416)	$ (79,088)	$ (155,939)	$ (40,471)	$ (85,964)	$ (157,957)
Net loss per share:
Basic (in dollars per share)	$ (0.11)	$ (0.11)	$ (0.08)	$ (0.06)	$ (0.06)	$ (0.14)	$ (0.33)	$ (0.24)	$ (0.14)	$ (0.25)	$ (0.71)		$ (0.36)	$ (0.77)	$ (1.46)
Diluted (in dollars per share)	$ (0.11)	$ (0.11)	$ (0.08)	$ (0.06)	$ (0.06)	$ (0.14)	$ (0.33)	$ (0.24)	$ (0.14)	$ (0.25)	$ (0.71)		$ (0.36)	$ (0.77)	$ (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	113,240	113,437	110,633		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	113,240	113,437	110,633		113,254	110,948	108,450