Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (12,138)	$ (15,383)	$ (25,543)	$ (31,470)
Other comprehensive gain:
Change in unrealized gain (loss) on available for sale investments, net of tax	11	38	19	190
Comprehensive loss	$ (12,127)	$ (15,345)	$ (25,524)	$ (31,280)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e557-108580

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Topic 944
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-Subparagraph (SX 210.7-04(18))
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-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
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-Paragraph 2
-Subparagraph (SX 210.5-03(20))
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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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