Sale of Decker Mine Interest (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Sale of Decker Mine Interest
Income Loss From Individually Significant Component Disposed Of Or Held For Sale Excluding Discontinued Operations Before Income Tax	$ 0	$ 74,262	$ 0	$ 74,262
Schedule Of Individually Significant Component Excluding Discontinued Operations [Line Items]
Ownership interest in Decker (as a percent)	50.00%		50.00%
Revenues	$ 301,673	342,337	$ 863,374	982,253
Costs and expenses	284,215	330,755	888,743	947,120
Operating income (loss)	17,458	85,844	(25,369)	109,395
Other income (expense)	(10,695)	45,900	(35,979)	(5,953)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	$ 6,763	131,744	$ (61,348)	103,442
Decker mine
Schedule Of Individually Significant Component Excluding Discontinued Operations [Line Items]
Revenues		6,095		15,653
Costs and expenses		5,774		19,475
Operating income (loss)		321		(3,823)
Other income (expense)		(13)		(41)
Income (loss) before income tax provision and earnings from unconsolidated affiliates		$ 309		$ (3,863)