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 represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets:
Short term investments:	$ 200,577	$ 129,314
Trading securities - energy industry	52,705	11,600
Available-for-sale equity securities
Assets:
Short term investments:	174,610	71,433
Recurring
Assets:
Trading securities - energy industry	52,705
Total short-term investments	253,282
Recurring \| Available-for-sale equity securities
Assets:
Short term investments:	174,610
Recurring \| Commercial paper and CDs
Assets:
Short term investments:	206
Recurring \| Corporate debt securities
Assets:
Short term investments:	23,399
Recurring \| Mortgage-backed debt securities
Assets:
Short term investments:	244
Recurring \| Mortgage-CMO debt securities
Assets:
Short term investments:	523
Recurring \| Asset-backed debt securities
Assets:
Short term investments:	1,595
Recurring \| Level 1
Assets:
Trading securities - energy industry	52,705
Total short-term investments	218,430
Recurring \| Level 1 \| Available-for-sale equity securities
Assets:
Short term investments:	163,924
Recurring \| Level 1 \| Commercial paper and CDs
Assets:
Short term investments:	206
Recurring \| Level 1 \| Asset-backed debt securities
Assets:
Short term investments:	1,595
Recurring \| Level 2
Assets:
Total short-term investments	34,852
Recurring \| Level 2 \| Available-for-sale equity securities
Assets:
Short term investments:	10,686
Recurring \| Level 2 \| Corporate debt securities
Assets:
Short term investments:	23,399
Recurring \| Level 2 \| Mortgage-backed debt securities
Assets:
Short term investments:	244
Recurring \| Level 2 \| Mortgage-CMO debt securities
Assets:
Short term investments:	$ 523