Debt and Capital Lease Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Long term debt and capital lease obligations
Current	$ 82,708		$ 82,708		$ 32,602
Non-current	53,974		53,974		115,861
Interest expenses incurred for various debt instruments
Accretion of Franco Nevada royalty obligation	5,559	5,770
Accretion expense on royalty obligation discount	5,600	5,800	10,663	11,037
Amortization of debt issuance costs	251	559	508	1,183
Accretion of debt discount	629	576	1,241	1,137
Capitalized interest	(610)	(238)	(1,694)	(415)
Total interest expense, net of capitalized interest	7,557	9,268	14,227	18,573
3.25% Convertible Senior Notes due March 2028 [Member]
Long term debt and capital lease obligations
Current	46,786		46,786		0
Non-current	0		0		45,545
Interest expenses incurred for various debt instruments
Interest Expense	395		791	791
Debt Instrument, Convertible, Interest Expense	400	395
1.25% Convertible Senior Notes due January 2024 [Member]
Interest expenses incurred for various debt instruments
Interest Expense	0	0	0	1
Senior Term Notes due December 31, 2012 [Member]
Interest expenses incurred for various debt instruments
Interest Expense	0	427	0	914
Kensington Term Facility [Member]
Long term debt and capital lease obligations
Current	24,248		24,248		15,398
Non-current	47,726		47,726		60,425
Interest expenses incurred for various debt instruments
Interest Expense	906	1,162	1,880	2,267
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Current	11,674		11,674		17,119
Non-current	6,248		6,248		9,891
Interest expenses incurred for various debt instruments
Interest Expense	265	472	608	938
Other Credit Derivatives [Member]
Long term debt and capital lease obligations
Current	0		0		85
Non-current	0		0		0
Other debt obligations [Member]
Interest expenses incurred for various debt instruments
Interest Expense	162	145	230	613
Gold lease facility [Member]
Interest expenses incurred for various debt instruments
Interest Expense	$ 0	$ 0	$ 0	$ 107