Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

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-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

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-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 50

-Paragraph 1

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-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 35

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

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-Name Accounting Standards Codification

-Topic 320

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Value of the not readily marketable security or category which has been determined by management based upon fair value methods, including pricing of similar securities and valuation techniques and is included in the schedule of financial condition or the balance sheet.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 820

-Section 50

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-Subparagraph (c)

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Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2013
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	$ 270,921us-gaap_AvailableForSaleSecurities	$ 359,097us-gaap_AvailableForSaleSecurities
Investment in non-marketable security
Impairment of Investment in non-marketable equity security	600	1,400	0
Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	124,938	300,605
Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	145,983	58,492
Fair Value, Measurements, Recurring [Member]
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	270,921	359,097
Fair Value, Measurements, Recurring [Member] \| Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	124,938	300,605
Fair Value, Measurements, Recurring [Member] \| Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	145,983	58,492
Fair Value, Measurements, Recurring [Member] \| Level 1
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	124,938	300,605
Fair Value, Measurements, Recurring [Member] \| Level 1 \| Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	124,938	300,605
Fair Value, Measurements, Recurring [Member] \| Level 1 \| Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	145,983	58,492
Fair Value, Measurements, Recurring [Member] \| Level 2 \| Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 2 \| Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	145,983	58,492
Fair Value, Measurements, Recurring [Member] \| Level 3
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Total available-for-sale securities	0	0
Nonrecurring basis
Investment in non-marketable security
Carrying Value	0	600		2,000
Impairment of Investment in non-marketable equity security	600	1,400
Nonrecurring basis \| Level 1
Investment in non-marketable security
Fair Value	0	0
Nonrecurring basis \| Level 2
Investment in non-marketable security
Fair Value	0	0
Nonrecurring basis \| Level 3
Investment in non-marketable security
Fair Value	$ 0	$ 600