Debt and Capital Lease Obligations (Details Textual) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended					3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Call Option [Member] oz	Dec. 31, 2012 Call Option [Member] oz	Sep. 30, 2013 Put Option [Member] oz	Dec. 31, 2012 Put Option [Member] oz	Sep. 30, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Sep. 30, 2012 3.25% Convertible Senior Notes due March 2028 [Member]	Sep. 30, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Sep. 30, 2012 3.25% Convertible Senior Notes due March 2028 [Member]	Feb. 12, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Dec. 31, 2012 3.25% Convertible Senior Notes due March 2028 [Member]	Sep. 30, 2013 7.875% Senior Notes due 2021 [Member]	Sep. 30, 2012 7.875% Senior Notes due 2021 [Member]	Sep. 30, 2013 7.875% Senior Notes due 2021 [Member]	Sep. 30, 2012 7.875% Senior Notes due 2021 [Member]	Jan. 29, 2013 7.875% Senior Notes due 2021 [Member]	Dec. 31, 2012 7.875% Senior Notes due 2021 [Member]	Sep. 30, 2013 Kensington Term Facility [Member]	Sep. 30, 2012 Kensington Term Facility [Member]	Sep. 30, 2013 Kensington Term Facility [Member]	Sep. 30, 2012 Kensington Term Facility [Member]	Sep. 30, 2013 Revolving Credit Facility [Member]	Sep. 30, 2012 Revolving Credit Facility [Member]	Sep. 30, 2013 Revolving Credit Facility [Member]	Sep. 30, 2012 Revolving Credit Facility [Member]
Debt and capital lease obligations (Textual) [Abstract]
Interest rate on notes										3.25%		3.25%			3.25%					7.875%
Principal amount of bank loan										$ 5,300,000		$ 5,300,000		$ 48,700,000						$ 300,000,000
Debt Instrument, Repurchased Face Amount										43,300,000		43,300,000
Debt, Current	3,868,000		3,868,000		55,983,000					0		0			48,081,000	0		0			0
Carrying value of the equity component										10,900,000		10,900,000			10,900,000
Interest expense										43,000	395,000	423,000	1,186,000
Interest Expense, Debt																5,906,000	0	15,947,000	0			0	459,000	0	2,339,000	176,000	85,000	434,000	85,000
Accretion of Debt Discount	0	639,000	576,000	1,879,000
Accretion expense	2,889,000	4,276,000	10,698,000	14,348,000
Long-term debt and capital leases	306,372,000		306,372,000		3,460,000					5,334,000		5,334,000			0	300,000,000		300,000,000			0
Borrowing under term facility	100,000,000		100,000,000
Line of Credit Facility, Increase, Additional Borrowings			50,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.50%
Line of Credit Facility, Commitment Fee Percentage			0.75%
Line of Credit Facility, Amount Outstanding	0		0
Gold under collars protection						12,500	97,000	25,000	122,000
Weighted average call feature of each collar					1,967.89
Weighted average put feature of each collar					967.86
Additional Long term debt and capital lease obligations(Textual) [Abstract]
Expensed Interest	9,662,000	7,351,000	30,324,000	21,578,000
Capitalized interest	$ 1,133,000	$ 512,000	$ 1,494,000	$ 2,206,000