Balance Sheet Account Detail (Held to Maturity Marketable Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 53,467	$ 59,871
Gross Unrealized Gain	7	5
Gross Unrealized Loss	3	8
Fair Value	53,471	59,868
Asset backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,473	3,633
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	1,473	3,633
Agency bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,000
Gross Unrealized Gain	0
Gross Unrealized Loss	1
Fair Value	2,999
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,669	15,707
Gross Unrealized Gain	0	0
Gross Unrealized Loss	2	8
Fair Value	5,667	15,699
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	40,281	40,531
Gross Unrealized Gain	7	5
Gross Unrealized Loss	0	0
Fair Value	40,288	40,536
Government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,044
Gross Unrealized Gain	0
Gross Unrealized Loss	0
Fair Value	3,044
Corporate debt securities
Schedule of Held-to-maturity Securities [Line Items]
Gross Unrealized Loss	3
Fair Value	$ 11,200
Held-to-maturity debt securities held	8

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

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

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

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-Name Accounting Standards Codification

-Topic 320

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