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Description of Business - Additional Information (Details) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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Description Of Business [Abstract] |  |
Accumulated deficit | $ (1,140,083) | $ (1,119,477)
Cash, cash equivalents and marketable securities | $ 66,300 |

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- Definition The cumulative amount of the reporting entity's undistributed earnings or deficit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.31(a)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 + Details
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