Unaudited Selected Quarterly Financial Data (Schedule Of Unaudited Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unaudited Selected Quarterly Financial Data [Abstract]
Total revenue	$ 19,526	$ 18,160	$ 21,578	$ 19,362	$ 24,935	$ 23,545	$ 20,073	$ 24,915	$ 78,626	$ 93,468	$ 90,714
Total gross profit	5,746	3,192	8,862	7,296	9,494	8,227	8,001	8,937	25,096	34,659	44,160
Total operating expenses	36,369	27,862	30,607	31,245	30,023	29,796	32,388	32,236	126,083	124,443	115,404
Loss from operations	(30,623)	(24,670)	(21,745)	(23,949)	(20,529)	(21,569)	(24,387)	(23,299)	(100,987)	(89,784)	(71,244)
Net loss	$ (30,799)	$ (25,044)	$ (22,540)	$ (24,179)	$ (20,762)	$ (22,021)	$ (25,539)	$ (23,867)	$ (102,562)	$ (92,189)	$ (74,375)
Basic and diluted net loss per share	$ (0.21)	$ (0.19)	$ (0.17)	$ (0.20)	$ (0.18)	$ (0.19)	$ (0.26)	$ (0.26)
Weighted average shares used in computing net loss per share	149,314	135,130	131,882	123,768	116,259	115,771	97,360	92,970	135,094	105,682	89,148

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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