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Stock Plans - Option Vesting (Details) - Stock options | 12 Months Ended
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Dec. 31, 2017
2000 Plan | First Anniversary |
Stockholder's Equity |
Percentage of awards vesting | 25.00%
2000 Plan | Monthly vesting after first anniversary |
Stockholder's Equity |
Percentage of awards vesting | 2.10%
2006 Plan | First Anniversary |
Stockholder's Equity |
Percentage of awards vesting | 25.00%
2006 Plan | Monthly vesting after first anniversary |
Stockholder's Equity |
Percentage of awards vesting | 2.10%
2015 Plan | First Anniversary |
Stockholder's Equity |
Percentage of awards vesting | 25.00%
2015 Plan | Monthly vesting after first anniversary |
Stockholder's Equity |
Percentage of awards vesting | 2.10%
2010 Plan | Second Anniversary |
Stockholder's Equity |
Percentage of awards vesting | 50.00%
2010 Plan | Monthly vesting after second anniversary |
Stockholder's Equity |
Percentage of awards vesting | 2.10%
2000 and 2006 Stock incentive plans | First Anniversary |
Stockholder's Equity |
Percentage of awards vesting | 25.00%
2000 and 2006 Stock incentive plans | Monthly vesting after first anniversary |
Stockholder's Equity |
Percentage of awards vesting | 2.10%

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- Definition Percentage of vesting of share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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