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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unaudited Selected Quarterly Financial Data [Abstract]
Total revenue	$ 24,935	$ 23,545	$ 20,073	$ 24,915	$ 25,722	$ 25,118	$ 20,747	$ 19,127	$ 93,468	$ 90,714	$ 92,782
Total gross profit	9,494	8,227	8,001	8,937	11,374	12,638	10,644	9,504	34,659	44,160	53,450
Total operating expenses	30,023	29,796	32,388	32,236	29,248	29,373	28,714	28,069	124,443	115,404	82,584
Loss from operations	(20,529)	(21,569)	(24,387)	(23,299)	(17,874)	(16,735)	(18,070)	(18,565)	(89,784)	(71,244)	(29,134)
Net loss	$ (20,762)	$ (22,021)	$ (25,539)	$ (23,867)	$ (19,030)	$ (17,494)	$ (18,499)	$ (19,352)	$ (92,189)	$ (74,375)	$ (31,696)
Basic and diluted net loss per share	$ (0.18)	$ (0.19)	$ (0.26)	$ (0.26)	$ (0.21)	$ (0.19)	$ (0.21)	$ (0.23)
Weighted average shares used in computing net loss per share	116,259	115,771	97,360	92,970	92,660	92,110	88,148	83,604	105,682	89,148	75,614

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1,2)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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