Investments (Available-For-Sale Investments) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	$ 146,799	$ 143,857	$ 137,222
Amortized Cost	146,821	143,857	137,189
Net Unrealized Gains (Losses)	(22)	0	33
Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	90,629	110,560	90,374
Amortized Cost	90,611	110,550	90,348
Net Unrealized Gains (Losses)	18	10	26
Government Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	31,565	24,394	36,165
Amortized Cost	31,565	24,399	36,153
Net Unrealized Gains (Losses)	0	(5)	12
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	24,605	8,903	10,683
Amortized Cost	24,645	8,908	10,688
Net Unrealized Gains (Losses)	$ (40)	$ (5)	$ (5)

- 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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