Concentration of Risks and Uncertainties (Details) $ in Thousands	Jun. 30, 2015 USD ($)
Concentration Risk [Line Items]
Corporate debt securities	$ 620,374
US Government Agencies Debt Securities
Concentration Risk [Line Items]
US Government Securities, at Carrying Value	259,600
Corporate debt securities
Concentration Risk [Line Items]
Corporate debt securities	103,900
Other Debt Obligations
Concentration Risk [Line Items]
Other Marketable Securities, Noncurrent	12,000
Commercial paper
Concentration Risk [Line Items]
Commercial Paper, at Carrying Value	$ 256,800

Amount of debt securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

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Unsecured short-term debt instrument issued by corporations which are highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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All other debt and equity financial instruments, which aren't categorized as available-for-sale, or held-to-maturity and which are not otherwise listed in the existing taxonomy, intended to be held longer than one year from the balance sheet date or the normal operating cycle, if longer.

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Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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