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Financial Instruments (Details 3) (USD $) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Proceeds from Marketable Debt Securities |  |
Proceeds from maturities and sales | $ 373,563,000 us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities | $ 757,512,000 us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities
Realized gains | 200,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | 200,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Realized losses | $ (300,000)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses | $ (100,000)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition The cash inflow associated with the sale or maturity (principal being due) of securities not classified as either held-to-maturity securities or trading securities which are classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26853-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 + Details
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