Investments (Available-for-Sale Investments) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Aggregate Fair Value	$ 147,136	$ 143,857	$ 134,266
Amortized Cost	147,142	143,857	134,219
Net Unrealized Gains (Losses)	(6)	0	47
Government Obligations [Member]
Aggregate Fair Value	100,679	110,560	90,440
Amortized Cost	100,664	110,550	90,416
Net Unrealized Gains (Losses)	15	10	24
Government Agency Obligations [Member]
Aggregate Fair Value	26,235	24,394	31,644
Amortized Cost	26,237	24,399	31,628
Net Unrealized Gains (Losses)	(2)	(5)	16
Corporate Obligations [Member]
Aggregate Fair Value	20,222	8,903	12,182
Amortized Cost	20,241	8,908	12,175
Net Unrealized Gains (Losses)	$ (19)	$ (5)	$ 7

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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