Marketable Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale securities
Amortized Cost	$ 158,241	$ 148,202
Gross Unrealized Gains	525	136
Gross Unrealized Losses	(1,220)	(1,782)
Total available-for-sale securities	157,546	146,556
State and municipal obligations [Member]
Available-for-sale securities
Amortized Cost	19,051	9,485
Gross Unrealized Gains	30	9
Gross Unrealized Losses	(5)	(12)
Total available-for-sale securities	19,076	9,482
Federal agency and corporate obligations [Member]
Available-for-sale securities
Amortized Cost	128,190	127,717
Gross Unrealized Gains	495	127
Gross Unrealized Losses	(4)	(335)
Total available-for-sale securities	128,681	127,509
Total short-term available-for-sale securities [Member]
Available-for-sale securities
Amortized Cost	147,241	137,202
Gross Unrealized Gains	525	136
Gross Unrealized Losses	(9)	(347)
Total available-for-sale securities	147,757	136,991
ARS, long-term [Member]
Available-for-sale securities
Amortized Cost	11,000	11,000
Gross Unrealized Gains
Gross Unrealized Losses	(1,211)	(1,435)
Total available-for-sale securities	$ 9,789	$ 9,565

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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