Debt and Capital Lease Obligations (Details Textual) (USD $)	3 Months Ended		12 Months Ended					3 Months Ended				3 Months Ended					0 Months Ended	3 Months Ended			0 Months Ended	3 Months Ended			3 Months Ended			0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Call Option [Member] oz	Dec. 31, 2012 Call Option [Member] oz	Mar. 31, 2013 Put Option [Member] oz	Dec. 31, 2012 Put Option [Member] oz	Mar. 31, 2013 3.25% Convertible Senior Notes due March 2028 [Member]	Mar. 31, 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]	Mar. 31, 2013 7.875% Senior Notes due 2021 [Member]	Mar. 31, 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]	Mar. 31, 2013 Debt After Step Down [Member]	Aug. 16, 2012 Kensington Term Facility [Member]	Mar. 31, 2013 Kensington Term Facility [Member] oz	Mar. 31, 2012 Kensington Term Facility [Member]	Mar. 31, 2012 Minimum [Member]	Jan. 29, 2013 Minimum [Member] 7.875% Senior Notes due 2021 [Member]	Mar. 31, 2013 LIBOR [Member]	Mar. 31, 2013 LIBOR [Member] Maximum [Member]	Mar. 31, 2013 LIBOR [Member] Minimum [Member]	Mar. 31, 2013 Alternate Base Rate [Member]	Mar. 31, 2013 Alternate Base Rate [Member] Maximum [Member]	Mar. 31, 2013 Alternate Base Rate [Member] Minimum [Member]	Jan. 29, 2013 Any time prior to February 1,2017 [Member] 7.875% Senior Notes due 2021 [Member]	Jan. 29, 2013 Any time prior to February 1,2017 [Member] Maximum [Member] 7.875% Senior Notes due 2021 [Member]	Jan. 29, 2013 Any time prior to February 1,2017 [Member] Minimum [Member] 7.875% Senior Notes due 2021 [Member]	Jan. 29, 2013 Ant time prior to February 1, 2016 [Member] 7.875% Senior Notes due 2021 [Member]
Debt and capital lease obligations (Textual) [Abstract]
Interest rate on notes								3.25%			3.25%			7.875%
Principal amount of bank loan								$ 5,300,000		$ 48,700,000				$ 300,000,000
Debt Instrument, Repurchased Face Amount								43,300,000
Current	6,130,000		55,983,000					0			48,081,000	0			0
Carrying value of the equity component								10,900,000			10,900,000
Interest expense								337,000	395,000
Interest Expense, Debt												4,134,000	0					0	974,000
Debt Instrument, Notice of Redemption																													60 days	30 days
Debt Instrument, Redemption Price, Percentage																												100.00%			107.875%
Debt Instrument, Event of Default, Percentage of Principal																					25.00%
Debt Instrument, Redemption Price, Percentage of Principal Amount																															35.00%
Accretion of Debt Discount	577,000	612,000
Accretion expense	3,670,000	4,580,000
Effective interest rate on the notes								8.90%
Long-term debt and capital leases	307,791,000		3,460,000					5,334,000			0	300,000,000			0
Borrowing under term facility	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
Debt Instrument, Basis Spread on Variable Rate																							3.25%	2.25%		2.25%	1.25%
Ratio of consolidated debt to adjusted EBITDA	3.25															3.00
Ratio of adjusted EBITDA to interest expense	3.00
Percentage of tangible net worth																				90.00%
Percentage of net income	25.00%
Line of Credit Facility, Amount Outstanding	0
Repayments of Long-term Debt																	68,600,000
Debt Instrument, Description of Variable Rate Basis																						LIBOR			alternate base rate
Protection of gold under gold hedging program																		243,750
Gold under collars protection				92,000	97,000	109,500	122,000
Weighted average call feature of each collar	1,966.14		1,967.89
Weighted average put feature of each collar	973.14		967.86
Outstanding amount of capital leases	8,600,000,000		11,400,000
Additional Long term debt and capital lease obligations(Textual) [Abstract]
Accretion expense on royalty obligation discount	4,100,000	5,100,000
Remaining Minimum Obligation Under Royalty Agreements	59,700,000		61,900,000
Expensed Interest	9,732,000	6,670,000
Capitalized interest	$ 393,000	$ 1,083,000