Debt and Capital Lease Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Long term debt and capital lease obligations
Current	$ 56,340		$ 56,340		$ 32,602
Non-current	5,053		5,053		115,861
Interest expenses incurred for various debt instruments
Accretion of Franco Nevada royalty obligation	4,384	5,370
Accretion expense on royalty obligation discount	4,400	5,400	15,047	16,407
Amortization of debt issuance costs	1,331	504	1,838	1,646
Accretion of debt discount	639	585	1,879	1,722
Capitalized interest	(512)	(886)	(2,206)	(1,302)
Total interest expense, net of capitalized interest	7,351	7,980	21,578	26,553
3.25% Convertible Senior Notes due March 2028 [Member]
Long term debt and capital lease obligations
Current	47,424		47,424		0
Non-current	0		0		45,545
Interest expenses incurred for various debt instruments
Interest Expense	395		1,186	1,186
Debt Instrument, Convertible, Interest Expense	400	395
Senior Term Notes due December 31, 2012 [Member]
Interest expenses incurred for various debt instruments
Interest Expense	0	366	0	1,280
Kensington Term Facility [Member]
Long term debt and capital lease obligations
Current	0		0		15,398
Non-current	0		0		60,425
Interest expenses incurred for various debt instruments
Interest Expense	459	1,086	2,339	3,353
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Current	8,916		8,916		17,119
Non-current	5,053		5,053		9,891
Interest expenses incurred for various debt instruments
Interest Expense	219	416	827	1,353
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	436	144	668	801
Gold lease facility [Member]
Interest expenses incurred for various debt instruments
Interest Expense	$ 0	$ 0	$ 0	$ 107