BENEFIT PLANS: (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
BENEFIT PLANS:
Number of Peruvian noncontributory defined benefit pension plans	2
Post retirement defined benefit plans
Defined benefit plan, net periodic benefit cost
Service cost	$ 0.7	$ 0.5
Interest cost	0.5	0.6
Expected return on plan assets	(1.8)	(1.8)
Amortization of net actuarial loss	(0.4)	(0.4)
Amortization of net loss (gain)	0.1	0.1
Net periodic benefit costs	(0.9)	(1.0)
Post-retirement health care plan
Defined benefit plan, net periodic benefit cost
Interest cost	0.8	0.7
Amortization of net loss (gain)		(0.2)
Net periodic benefit costs	0.8	0.5
Post-retirement health care plan | Maximum
Defined benefit plan, net periodic benefit cost
Amortization of net loss (gain)	0.1
Amortization of prior service cost (credit)	$ 0.1	$ 0.1