Long-Term Debt and Capital Lease Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Long term debt and capital lease obligations
Current	$ 80,857		$ 32,602
Non-current	63,934		115,861
Interest expenses incurred for various debt instruments
Accretion of Franco Nevada royalty obligation	5,104	5,267
Amortization of debt issuance costs	256	624
Accretion of debt discount	612	560
Capitalized interest	(1,083)	(178)
Total interest expense, net of capitalized interest	6,670	9,304
3.25% Convertible Senior Notes due March 2028 [Member]
Long term debt and capital lease obligations
Current	46,157		0
Non-current	0		45,545
Interest expenses incurred for various debt instruments
Interest Expense	395	395
1.25% Convertible Senior Notes due January 2024 [Member]
Interest expenses incurred for various debt instruments
Interest Expense	0	1
Senior Term Notes due December 31, 2012 [Member]
Interest expenses incurred for various debt instruments
Interest Expense	0	488
Kensington Term Facility [Member]
Long term debt and capital lease obligations
Current	21,747		15,398
Non-current	54,075		60,425
Interest expenses incurred for various debt instruments
Interest Expense	974	1,105
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Current	12,953		17,119
Non-current	9,859		9,891
Interest expenses incurred for various debt instruments
Interest Expense	343	466
Other [Member]
Long term debt and capital lease obligations
Current	0		85
Non-current	0		0
Other debt obligations [Member]
Interest expenses incurred for various debt instruments
Interest Expense	69	469
Gold lease facility [Member]
Interest expenses incurred for various debt instruments
Interest Expense	$ 0	$ 107