Sale of Decker Mine Interest (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
Sale of Decker Mine interests
Ownership interest in Decker (as a percent)	50.00%
Income Loss From Individually Significant Component Disposed Of Or Held For Sale Excluding Discontinued Operations Before Income Tax	$ 0	$ 74,300	$ 0
Individually Significant Component Results of Operations
Revenues	317,553		319,066
Costs and expenses	309,569		302,942
Operating income (loss)	7,984		16,124
Other income (expense)	(12,956)		(38,335)
Income (loss) before income tax provision and earnings from unconsolidated affiliates	(4,972)		(22,211)
Decker mine
Individually Significant Component Results of Operations
Revenues			3,965
Costs and expenses			5,972
Operating income (loss)			(2,007)
Other income (expense)			(14)
Income (loss) before income tax provision and earnings from unconsolidated affiliates			$ (2,021)