Short-term Investments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 90,648	$ 8,427
Available-for-sale securities, gross unrealized gains	20	169
Available-for-sale securities, gross unrealized losses	(1,193)	(1,999)
Available-for-sale securities, fair value	89,475	6,597
Fluctuation in equity securites, gross unrealized gains	0.60
Fluctuation in equity securites, gross unrealized losses	(0.42)
Available-for-sale Securities, Gross Realized Gains	31
Available-for-sale Securities, Gross Realized Losses	555
Proceeds from Sale and Maturity of Marketable Securities	319,811	0	0
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	87,394
Available-for-sale securities, gross unrealized gains	20
Available-for-sale securities, gross unrealized losses	(411)
Available-for-sale securities, fair value	87,003
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	3,254	8,427
Available-for-sale securities, gross unrealized gains	0	169
Available-for-sale securities, gross unrealized losses	(782)	(1,999)
Available-for-sale securities, fair value	$ 2,472	$ 6,597
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Maturity Date	Dec. 31, 2013
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment Maturity Date	Dec. 31, 2014

Fluctuation in equity securites, gross unrealized gains

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Fluctuation in equity securites, gross unrealized losses

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- Definition

The maturity date of the investment.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 12

-Sentence Column A

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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-Name FASB Staff Position (FSP)

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- Definition

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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-Name Accounting Standards Codification

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-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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-Name Accounting Standards Codification

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

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