Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	$ 492,298	$ 494,122
Short-term Investments [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	27,947	33,137
Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	221,025	222,198
Fair Value, Inputs, Level 1 [Member] \| Short-term Investments [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	27,947	33,137
Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	271,273	271,924
Fair Value, Inputs, Level 2 [Member] \| Short-term Investments [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	0	0
Municipal [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	21,247	27,801
Municipal [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	0	0
Municipal [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	21,247	27,801
Corporate and utilities [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	250,026	244,123
Corporate and utilities [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	0	0
Corporate and utilities [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	250,026	244,123
Foreign [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	163,637	164,268
Foreign [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	163,637	164,268
Foreign [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	0	0
U.S. Government [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	19,173	19,350
U.S. Government [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	19,173	19,350
U.S. Government [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	0	0
Equity securities [Member]
Financial instruments measured at fair value on a recurring basis
Investments, Fair value measurements	10,268	5,443
Equity securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	10,268	5,443
Equity securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Financial instruments measured at fair value on a recurring basis
Available-for-sale securities, Fair value measurements	$ 0	$ 0

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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