Cash and Cash Equivalents and Short-term Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Cash and cash equivalents and short-term investments
Cash and cash equivalents, fair value	$ 501,149	$ 389,915
Available-for-sale equities securities
Available-for-sale equity securities, fair value	35,020us-gaap_AvailableForSaleSecurities	117,218us-gaap_AvailableForSaleSecurities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	18	20,276
Available-for-sale securities, gross unrealized holding gains	14,648	72,530
Available-for-sale securities, gross unrealized holding losses	(1)	(56)
Total short-term investments	35,020us-gaap_ShortTermInvestments	117,218us-gaap_ShortTermInvestments
Total cash, cash equivalents and short-term investments, fair value	536,169	507,133
Total cash, cash equivalents and short-term investments, gross unrealized gains	14,648	72,530
Total cash, cash equivalents and short-term investments, gross unrealized losses	(1)	(56)
Equity Securities
Available-for-sale equities securities
Available-for-sale equity securities, fair value	35,002	96,942
Available-for-sale debt securities:
Available-for-sale securities, gross unrealized holding gains	14,648	68,395
Debt Securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	18	20,276
Available-for-sale securities, gross unrealized holding gains		4,135
Available-for-sale securities, gross unrealized holding losses	(1)	(56)
Corporate Debt Securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value		19,388
Available-for-sale securities, gross unrealized holding gains		4,122
Collateralized Mortgage Backed Securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value		210
Available-for-sale securities, gross unrealized holding gains		11
Collateralized Debt Obligations
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	18	20
Available-for-sale securities, gross unrealized holding losses	(1)	(2)
Asset-backed Securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value		658
Available-for-sale securities, gross unrealized holding gains		2
Available-for-sale securities, gross unrealized holding losses		(54)
Short-term Investments.
Available-for-sale debt securities:
Available-for-sale securities, gross unrealized holding gains	14,648	72,530
Available-for-sale securities, gross unrealized holding losses	(1)	(56)
Total short-term investments	$ 35,020	$ 117,218

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Amount of accumulated unrealized gain before deducting unrealized loss on investments in available-for-sale securities impacting investments.

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Amount of accumulated unrealized loss before deducting unrealized gain on investments in available-for-sale securities impacting investments.

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

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Amount of investments in debt securities classified as available-for-sale, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal 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. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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