Debt and Capital Lease Obligations (Details Textual) (USD $)	3 Months Ended			6 Months Ended		12 Months Ended					3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Call Option [Member] oz	Dec. 31, 2012 Call Option [Member] oz	Jun. 30, 2013 Put Option [Member] oz	Dec. 31, 2012 Put Option [Member] oz	Jun. 30, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Jun. 30, 2012 3.25% Convertible Senior Notes due March 2028 [Member]	Jun. 30, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Jun. 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]	Jun. 30, 2013 7.875% Senior Notes due 2021 [Member]	Jun. 30, 2012 7.875% Senior Notes due 2021 [Member]	Jun. 30, 2013 7.875% Senior Notes due 2021 [Member]	Jun. 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]	Jun. 30, 2013 Kensington Term Facility [Member]	Jun. 30, 2012 Kensington Term Facility [Member]	Jun. 30, 2013 Kensington Term Facility [Member]	Jun. 30, 2012 Kensington Term Facility [Member]
Debt and capital lease obligations (Textual) [Abstract]
Interest rate on notes											3.25%		3.25%			3.25%	7.875%		7.875%		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
Current	5,485,000			5,485,000		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	380,000	791,000
Interest Expense, Debt																	5,906,000	0	10,041,000	0			0	906,000	0	1,880,000
Accretion of Debt Discount	0	629,000		576,000	1,241,000
Accretion expense	4,139,000	5,492,000		7,809,000	10,072,000
Long-term debt and capital leases	306,578,000			306,578,000		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				0.10%
Line of Credit Facility, Commitment Fee Amount	0.1			0.3
Line of Credit Facility, Amount Outstanding	0			0
Gold under collars protection							87,000	97,000	97,000	122,000
Weighted average call feature of each collar	1,964.20					1,967.89
Weighted average put feature of each collar	979.79					967.86
Additional Long term debt and capital lease obligations(Textual) [Abstract]
Accretion expense on royalty obligation discount	4,100,000		5,600,000	8,170,000	10,663,000
Remaining Minimum Obligation Under Royalty Agreements	56,500,000			56,500,000		61,900,000
Current portion of minimum obligation under royalty agreement	23,900,000			23,900,000		24,000,000
Expensed Interest	10,930,000	7,557,000		20,662,000	14,227,000
Capitalized interest	$ (32,000)	$ 610,000		$ 361,000	$ 1,694,000