Investments (Summary Of Investments Current And Non-Current) (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Schedule of Investments [Line Items]
Total current investments	$ 150,135,000	$ 264,572,000
Total non-current investments	2,226,875,000	3,832,659,000
FMG Zero Coupon Note Component [Member]
Schedule of Investments [Line Items]
Other investments - non-current	40,801,000
Amortized Cost [Member]
Schedule of Investments [Line Items]
Investments available for sale - current	146,594,000	253,273,000
Other investments, including accrued interest income	4,113,000	11,067,000
Total current investments	150,707,000	264,340,000
Total non-current investments	1,517,649,000	1,958,287,000
Amortized Cost [Member] \| Fortescue [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	115,703,000	219,723,000
Amortized Cost [Member] \| Inmet Mining Corporation [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	504,006,000	504,006,000
Amortized Cost [Member] \| Other Investments Available For Sale [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	724,664,000	1,067,928,000
Amortized Cost [Member] \| Private Equity Funds [Member]
Schedule of Investments [Line Items]
Other investments - non-current	85,528,000	86,944,000
Amortized Cost [Member] \| Non-Agency Mortgage-Backed Bond Securitization Portfolio [Member]
Schedule of Investments [Line Items]
Other investments - non-current	1,649,000	3,304,000
Amortized Cost [Member] \| FMG Zero Coupon Note Component [Member]
Schedule of Investments [Line Items]
Other investments - non-current	40,801,000	36,268,000
Amortized Cost [Member] \| Other Non-Publicly Traded Investments [Member]
Schedule of Investments [Line Items]
Other investments - non-current	45,298,000	40,114,000
Carrying Value And Estimated Fair Value [Member]
Schedule of Investments [Line Items]
Investments available for sale - current	145,977,000	253,589,000
Other investments, including accrued interest income	4,158,000	10,983,000
Total current investments	150,135,000	264,572,000
Total non-current investments	2,226,875,000	3,832,659,000
Carrying Value And Estimated Fair Value [Member] \| Fortescue [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	569,256,000	1,659,617,000
Carrying Value And Estimated Fair Value [Member] \| Inmet Mining Corporation [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	708,193,000	862,481,000
Carrying Value And Estimated Fair Value [Member] \| Other Investments Available For Sale [Member]
Schedule of Investments [Line Items]
Investments available for sale - non-current	776,444,000	1,144,141,000
Carrying Value And Estimated Fair Value [Member] \| Private Equity Funds [Member]
Schedule of Investments [Line Items]
Other investments - non-current	85,528,000	86,944,000
Carrying Value And Estimated Fair Value [Member] \| Non-Agency Mortgage-Backed Bond Securitization Portfolio [Member]
Schedule of Investments [Line Items]
Other investments - non-current	1,649,000	3,304,000
Carrying Value And Estimated Fair Value [Member] \| FMG Zero Coupon Note Component [Member]
Schedule of Investments [Line Items]
Other investments - non-current	40,801,000	36,268,000
Carrying Value And Estimated Fair Value [Member] \| Other Non-Publicly Traded Investments [Member]
Schedule of Investments [Line Items]
Other investments - non-current	$ 45,004,000	$ 39,904,000

Investments in debt and equity securities which are categorized neither as trading securities nor held-to-maturity securities and which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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+ Details

- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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+ Details