Financial Instruments - Available For Sale Securities (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Schedule of Investments [Line Items]
Realized security gains	$ 9,500,000	$ 2,526,000	$ 239,391,000	$ 427,462,000
Unrealized loss on investments	65,519,000		65,519,000		2,208,000
Inmet Mining Corporation [Member]
Schedule of Investments [Line Items]
Shares of common stock owned					11,042,413
Percentage of outstanding shares					15.90%
Realized security gains			227,600,000
Aggregate net proceeds			391,200,000
First Quantum Minerals Ltd [Member]
Schedule of Investments [Line Items]
Shares of common stock received			18,202,313
Fair value of shares received			340,400,000
Number of shares sold	2,413,713
Unrealized loss on investments	61,100,000		61,100,000
Aggregate net proceeds	$ 44,900,000