Investments (Available-For-Sale Investments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	$ 114,806	$ 148,488	$ 147,267
Amortized Cost	114,808	148,467	147,319
Net Unrealized Gains (Losses)	(2)	21	(52)
Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	80,445	100,517	100,658
Amortized Cost	80,446	100,480	100,691
Net Unrealized Gains (Losses)	(1)	37	(33)
Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	17,022	31,351	33,172
Amortized Cost	17,022	31,354	33,187
Net Unrealized Gains (Losses)	0	(3)	(15)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	17,339	16,620	13,437
Amortized Cost	17,340	16,633	13,441
Net Unrealized Gains (Losses)	$ (1)	$ (13)	$ (4)

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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