| Consolidated Statement of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016 | |
| Statement of Comprehensive Income [Abstract] | ||||
| Other comprehensive income (loss), Unrealized Holding Gain (Loss) on Securities Arising During the Period, tax | $ 0 | $ 0 | $ 0 | $ 0 | 
| Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax | 0 | 0 | 0 | 0 | 
| Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax | $ 13 | $ 41 | $ 68 | $ 68 | 
| X | ||||||||||
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- Definition Amount of tax expense (benefit), after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- References No definition available. 
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