Sale of Decker Mine Interest (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 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	$ 74,300	$ 0
Schedule Of Individually Significant Component Excluding Discontinued Operations [Line Items]
Ownership interest in Decker (as a percent)	50.00%			50.00%
Revenues	$ 244,148		320,850	$ 561,701	$ 639,916
Costs and expenses	294,960		313,422	604,529	616,365
Operating income (loss)	(50,812)		7,428	(42,828)	23,551
Other income (expense)	(12,327)		(13,519)	(25,283)	(51,853)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	$ (63,139)		(6,091)	$ (68,111)	(28,302)
Decker mine
Schedule Of Individually Significant Component Excluding Discontinued Operations [Line Items]
Revenues			5,592		9,557
Costs and expenses			7,730		13,701
Operating income (loss)			(2,137)		(4,144)
Other income (expense)			(14)		(28)
Income (loss) before income tax provision and earnings from unconsolidated affiliates			$ (2,151)		$ (4,172)