Derivative Gains And Losses (Details) In Thousands, except Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended
	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 Riverstone Resources, Inc. - warrants USD ($)	Jun. 30, 2011 Riverstone Resources, Inc. - warrants USD ($)	Mar. 31, 2008 Riverstone Resources, Inc. - warrants CAD	Jun. 30, 2012 Riverstone Resources, Inc. - warrants USD ($)	Jun. 30, 2011 Riverstone Resources, Inc. - warrants USD ($)	Jun. 30, 2012 Gold price derivatives USD ($)	Jun. 30, 2011 Gold price derivatives USD ($)	Jun. 30, 2012 Gold price derivatives USD ($)	Jun. 30, 2011 Gold price derivatives USD ($)	Feb. 28, 2011 Gold price derivatives oz	Jan. 31, 2011 Gold price derivatives oz	Jun. 30, 2012 Riverstone Resources, Inc. - warrants and Gold Price derivatives USD ($)	Jun. 30, 2011 Riverstone Resources, Inc. - warrants and Gold Price derivatives USD ($)	Jun. 30, 2012 Riverstone Resources, Inc. - warrants and Gold Price derivatives USD ($)	Jun. 30, 2011 Riverstone Resources, Inc. - warrants and Gold Price derivatives USD ($)
Derivative [Line Items]
Derivative (gain) / loss	$ 0	$ 2,430	$ 162	$ 6,679	$ 0	$ 315		$ 162	$ 41	$ 0	$ 2,115	$ 0	$ 6,638
Realized (gain) / loss																0	1,499	(393)	1,499
Unrealized (gain)/loss	$ 0	$ (930)	$ (162)	$ (5,179)												$ 0	$ 931	$ 555	$ 5,180
Warrants issued							2
Warrants exercise price (CDN$ per share)							0.45
Notional amount of derivative (ounces)														75,200	76,800
Derivative floor price (US$ per ounce)														1,200	1,200
Derivative cap price (US$ per ounce)														1,503	1,457