Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Continuous unrealized loss position, Fair Value
Fair Value, Total	$ 105,560	$ 245,320
Continuous unrealized loss position, Gross Unrealized Loss
Gross Unrealized Loss, Total	(147)	(240)
Government-sponsored enterprises
Continuous unrealized loss position, Fair Value
Less than one year, Fair value	15,293	76,651
Fair Value, Total	15,293	76,651
Continuous unrealized loss position, Gross Unrealized Loss
Less than one year, Gross Unrealized Loss	(39)	(77)
Gross Unrealized Loss, Total	(39)	(77)
Corporate notes and bonds
Continuous unrealized loss position, Fair Value
Less than one year, Fair value	86,824	168,669
Fair Value, Total	90,267	168,669
Greater than one year, Fair value	3,443
Continuous unrealized loss position, Gross Unrealized Loss
Less than one year, Gross Unrealized Loss	(97)	(163)
Gross Unrealized Loss, Total	(108)	(163)
Greater than one year, Gross Unrealized Loss	$ (11)

Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for twelve months or longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Name Accounting Standards Codification

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity that have been in a continuous loss position for less than twelve months.

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