Cash and Cash Equivalents and Investments in Marketable Securities (Available-For-Sale Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 635,730	$ 261,489
Available-for-Sale Securities, Gross Unrealized Gain	59	217
Available-for-sale Securities, Gross Unrealized Losses	(87)	0
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)	635,702	261,706
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost		610
Available-for-Sale Securities, Gross Unrealized Gain		143
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)		753
Certificates of deposit
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost	82,791
Available-for-Sale Securities, Gross Unrealized Gain	14
Available-for-sale Securities, Gross Unrealized Losses	(6)
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)	82,799
Commercial paper
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost	45,737
Available-for-Sale Securities, Gross Unrealized Gain	17
Available-for-sale Securities, Gross Unrealized Losses	0
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)	45,754
Corporate debt securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost	49,587
Available-for-Sale Securities, Gross Unrealized Gain	2
Available-for-sale Securities, Gross Unrealized Losses	(30)
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)	49,559
State and political subdivisions debt securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-Sale Securities, Amortized Cost	457,615	260,879
Available-for-Sale Securities, Gross Unrealized Gain	26	74
Available-for-sale Securities, Gross Unrealized Losses	(51)	0
Available-for-Sale Securities, Estimated Fair Value (Net Carrying Amount)	$ 457,590	$ 260,953

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.

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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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- Definition

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

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