WORKERS' PARTICIPATION: (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statutory workers' participation
Workers' participation expense (in USD)	$ 276.7	$ 234.4	$ 134.7
Peru
Statutory workers' participation
Provision for workers' participation as a percentage of pre-tax earnings	8.00%
Number of months for which an individual worker's salary is capped for consideration of annual individual worker participation	18
Maximum taxable units contributed by employer to benefit fund (in Peruvian taxable units)	2,200
Maximum employer contribution to benefit fund (in USD)	$ 2.9
Mexican Operations.
Statutory workers' participation
Provision for workers' participation as a percentage of pre-tax earnings	10.00%