Cash and Cash Equivalents and Short-term Investments (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Cash and cash equivalents and short-term investments
Cash and cash equivalents, fair value	$ 398,575	$ 641,702
Short-term investments:
Trading equity securities, fair value	11,600	19,630
Trading equity securities, gross unrealized holding gains	5,876	13,906
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	57,881	60,160
Total available-for-sale debt securities, gross unrealized losses	0
Available-for-sale equities securities
Available-for-sale equity securities - energy industry	129,314	139,858
Available-for-sale equity securities, gross unrealized holding gains	55,592	53,487
Available-for-sale equity securities, gross unrealized holding losses	(2,348)	(2,566)
Total short-term investments	140,914	159,488
Total cash, cash equivalents and short-term investments, fair value	539,489	801,190
Total cash, cash equivalents and short-term investments, gross unrealized gains	61,468	67,393
Total cash, cash equivalents and short-term investments, gross unrealized losses	(2,348)	(2,566)
Debt Securities [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	57,881	60,160
Total available-for-sale debt securities, gross unrealized gains	22,517	15,311
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses	(2,348)	(292)
Equity Securities [Member]
Available-for-sale equities securities
Available-for-sale equity securities - energy industry	71,433	79,698
Available-for-sale equity securities, gross unrealized holding gains	33,075	38,176
Available-for-sale equity securities, gross unrealized holding losses	0	(2,274)
Commercial paper and CDs [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	1,230	1,275
Total available-for-sale debt securities, gross unrealized gains	0
Total available-for-sale debt securities, gross unrealized losses	0
Corporate debt securities [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	51,300	52,022
Total available-for-sale debt securities, gross unrealized gains	22,494	15,274
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses	(2,095)	(18)
Mortgage-backed debt securities [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	309	372
Total available-for-sale debt securities, gross unrealized gains	10	16
Total available-for-sale debt securities, gross unrealized losses	0
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses		0
Mortgage-CMO debt securities [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	2,547	3,015
Total available-for-sale debt securities, gross unrealized gains	13	21
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses	(15)	(6)
Asset-backed debt securities [Member]
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	2,495	3,476
Total available-for-sale debt securities, gross unrealized gains	0
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses	(238)	(268)
Short-term Investments [Member]
Available-for-sale equities securities
Available-for-sale equity securities, gross unrealized holding losses	(2,348)	(2,566)
Total short-term investments	140,914	159,488
Total short-term investments, gross unrealized gains	$ 61,468	$ 67,393

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Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item 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 Company may deposit additional funds at any time and also 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.

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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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