Balance Sheet Account Detail (Held-to Maturity Marketable Securities) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($) securities	Dec. 31, 2014 USD ($)
Marketable Securities [Abstract]
Amortized Cost	$ 52,768	$ 59,871
Gross Unrealized Gain	1	5
Gross Unrealized Loss	(53)	(8)
Fair Value	$ 52,716	59,868
Held to maturity securities, number of securities held \| securities	12
Total unrealized loss, securities in unrealized loss position	$ 53
Fair value of investments, unrealized loss position	44,700
Agency bonds
Marketable Securities [Abstract]
Amortized Cost	8,000	3,633
Gross Unrealized Gain	0	0
Gross Unrealized Loss	(20)	0
Fair Value	7,980	3,633
Government securities
Marketable Securities [Abstract]
Amortized Cost	40,824	15,707
Gross Unrealized Gain	1	0
Gross Unrealized Loss	(33)	(8)
Fair Value	40,792	15,699
Commercial paper
Marketable Securities [Abstract]
Amortized Cost	3,944	40,531
Gross Unrealized Gain	0	5
Gross Unrealized Loss	0	0
Fair Value	$ 3,944	$ 40,536

Held to Maturity Securities, Number of Securities Held

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

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

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Amount before other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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Fair value of investments in debt securities classified as held-to-maturity.

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Amount of unrealized loss before deducting unrealized gain on investments in held-to-maturity securities that have been in a loss position for less than twelve months.

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