BENEFIT PLANS: - Other (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) plan	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Benefit plans
Number of noncontributory defined benefit pension plans | plan	2
Post retirement defined benefit plans and defined contribution plan
Defined benefit plan, net periodic benefit costs
Service cost	$ 1.1	$ 1.0	$ 0.8
Interest cost	1.8	1.6	1.4
Expected return on plan assets	(3.5)	(3.4)	(2.9)
Amortization of prior service cost (credit)	0.2	0.2	0.1
Settlement / Curtailment		(0.2)	0.1
Amortization of net loss (gain)	0.3	0.2	0.2
Net periodic benefit cost	(0.1)	(0.6)	(0.3)
Change in benefit obligation:
Projected benefit obligation at beginning of year	27.4	27.5
Service cost	1.1	1.0	0.8
Interest cost	1.8	1.6	1.4
Benefits paid	(1.8)	(1.6)
Actuarial (gain)/loss	3.6	(0.2)
Actuarial gain assumption changes	0.9	(0.8)
Inflation adjustment	0.7	(0.1)
Projected benefit obligation at end of year	33.7	27.4	27.5
Change in plan assets:
Fair value of plan assets at beginning of year	46.7	51.6
Actual return on plan assets	4.8	(3.5)
Employer contributions	(0.6)	(0.4)
Benefits paid	(0.9)	(1.0)
Currency exchange rate adjustment	1.6
Fair value of plan assets at end of year	51.6	46.7	51.6
Funded status at end of year				$ 17.9	$ 19.3
Amounts recognized in statement of financial position
Non-current assets				17.9	19.4
Total				17.9	19.4
Amounts recognized in accumulated other comprehensive income
Net loss (gain)				7.6	5.8
Prior service cost (credit)				1.4	1.4
Total, net of tax	7.2	7.2	3.8	9.0	7.2
Net loss (gain), income taxes				(5.4)	(4.3)
Reconciliation of accumulated other comprehensive income:
Accumulated other comprehensive income at beginning of plan year	7.2	3.8
Net loss/(gain) amortized during the year	1.9	3.6
Net loss/(gain) occurring during the year	(0.2)	(0.1)
Currency exchange rate adjustment	0.1	(0.1)
Net adjustment to accumulated other comprehensive income	1.8	3.4
Accumulated other comprehensive income at end of plan year	9.0	7.2	$ 3.8
Net adjustment to accumulated other comprehensive income, income taxes	(2.2)	(2.2)
Amounts in accumulated other comprehensive income amortized and recognized as a component of net periodic benefit cost, net of income tax
Net loss / (gain)	1.8	3.6
Amortization of net (loss) gain	(0.2)	(0.1)
Total amortization expenses	$ 1.6	$ 3.5
Expected Benefit Payments
2020				3.2
2021				1.9
2022				2.0
2023				2.0
2024				2.3
2025 to 2027				14.7
Total				26.1
Post retirement defined benefit plans and defined contribution plan | Expatriate Plan
Assumptions used to determine the pension obligation and other post-retirement benefits and cost
Discount rate (as a percent)	2.85%	3.90%	3.25%
Expected long-term rate of return on plan asset (as a percent)	4.00%	4.00%	4.00%
Post retirement defined benefit plans and defined contribution plan | Mexican Health Plan
Assumptions used to determine the pension obligation and other post-retirement benefits and cost
Discount rate (as a percent)	7.15%	8.45%	7.80%
Expected long-term rate of return on plan asset (as a percent)	7.15%	8.45%	7.55%
Rate of increase in future compensation level (as a percent)	4.50%	4.50%	4.50%
Post-retirement Health care plans
Defined benefit plan, net periodic benefit costs
Interest cost	$ 0.9	$ 0.9	$ 0.9
Amortization of prior service cost (credit)	(0.2)	(0.2)	(0.2)
Net periodic benefit cost	0.7	0.7	0.7
Change in benefit obligation:
Projected benefit obligation at beginning of year	11.9	12.5
Interest cost	0.9	0.9	0.9
Actuarial loss/ (gain) - claims cost		0.2
Benefits paid	(1.3)	(0.9)
Actuarial (gain)/loss	8.6	(0.9)
Inflation adjustment	0.5	0.1
Projected benefit obligation at end of year	20.6	11.9	12.5
Change in plan assets:
Employer contributions	(0.1)	(0.1)
Benefits paid	(0.1)	(0.1)
Funded status at end of year				20.6	11.9
Amounts recognized in statement of financial position
Current liabilities				(0.1)	(0.1)
Non-current liabilities				(20.5)	(11.8)
Total				(20.6)	(11.9)
Amounts recognized in accumulated other comprehensive income
Net loss (gain)				1.5	(4.4)
Total, net of tax	(4.4)	(3.9)	(3.9)	1.5	(4.4)
Net loss (gain), income taxes				(0.7)	$ 1.9
Reconciliation of accumulated other comprehensive income:
Accumulated other comprehensive income at beginning of plan year	(4.4)	(3.9)
Net loss/(gain) amortized during the year	0.1	0.1
Net loss/(gain) occurring during the year	6.0	(0.6)
Currency exchange rate adjustment	(0.2)
Net adjustment to accumulated other comprehensive income	5.9	(0.5)
Accumulated other comprehensive income at end of plan year	1.5	(4.4)	$ (3.9)
Net adjustment to accumulated other comprehensive income, income taxes	(2.6)	0.2
Amounts in accumulated other comprehensive income amortized and recognized as a component of net periodic benefit cost, net of income tax
Net loss / (gain)	5.9	(0.6)
Amortization of net (loss) gain	0.2	0.2
Total amortization expenses	$ 6.1	$ (0.4)
Expected Benefit Payments
2020				1.3
2021				1.3
2022				1.3
2023				1.4
2024				1.4
2025 to 2029				7.3
Total				$ 14.0
Post-retirement Health care plans | Expatriate Plan
Assumptions used to determine the pension obligation and other post-retirement benefits and cost
Discount rate (as a percent)	2.85%	3.90%	3.25%
Expected Benefit Payments
Assumed trend rate for covered health care benefit cost (as a percent)	5.80%
Assumed trend rate for covered health care benefit cost post-65 years of age (as a percent)	5.20%
Assumed ultimate trend rate for health care benefit cost (as a percent)				4.20%
Assumed ultimate trend rate for health care benefit cost post-65 years of age (as a percent)	4.00%
Post-retirement Health care plans | Mexican Health Plan
Expected Benefit Payments
Assumed trend rate for covered health care benefit cost (as a percent)		4.50%
Effect of one percentage-point change in assumed other benefit cost trend rates
Effect of one percentage-point increase on total service and interest cost components	$ 1.4
Effect of one percentage-point decrease on total service and interest cost components	0.9
Effect of one percentage-point increase on post-retirement benefit obligation	18.8
Effect of one percentage-point decrease on post-retirement benefit obligation	$ 12.2
Post-retirement Health care plans | Weighted average | Mexican Health Plan
Assumptions used to determine the pension obligation and other post-retirement benefits and cost
Discount rate (as a percent)	7.15%	8.45%	7.80%