BENEFIT PLANS: - Other (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) plan	Dec. 31, 2020 USD ($)	Dec. 31, 2019 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	$ 1.4	$ 1.4	$ 1.1
Interest cost	1.5	1.7	1.8
Expected return on plan assets	(3.3)	(2.9)	(3.5)
Amortization of net actuarial loss	(0.1)	0.1
Amortization of prior service cost / (credit)	0.2	0.2	0.2
Settlement / Curtailment		(0.4)
Amortization of net loss/(gain)	0.3	0.2	0.3
Net periodic benefit cost		0.3	(0.1)
Change in benefit obligation:
Projected benefit obligation at beginning of year	29.9	33.7
Service cost	1.4	1.4	1.1
Interest cost	1.5	1.7	1.8
Benefits paid	(2.2)	(1.9)
Actuarial (gain)/loss	6.7	(4.2)
Actuarial gain assumption changes	(0.4)	0.8
Inflation adjustment	(0.6)	(1.6)
Projected benefit obligation at end of year	36.3	29.9	33.7
Change in plan assets:
Fair value of plan assets at beginning of year	54.4	51.6
Actual return on plan assets	4.3	6.5
Employer contributions	(0.6)	(0.6)
Benefits paid	(0.8)	(0.9)
Currency exchange rate adjustment	(1.3)	(2.2)
Fair value of plan assets at end of year	56.0	54.4	51.6
Funded status at end of year	19.7	24.5
Amounts recognized in statement of financial position
Non-current assets	19.7	24.5
Total	19.7	24.5
Amounts recognized in accumulated other comprehensive income
Net loss (gain)	6.2	3.0
Prior service cost (credit)	1.0	1.2
Total, net of tax	7.2	4.2	9.0
Net loss (gain), income taxes	(4.2)	(2.3)
Reconciliation of accumulated other comprehensive income:
Accumulated other comprehensive income at beginning of plan year	4.2	9.0
Net loss/(gain) amortized during the year	3.3	(4.1)
Net loss/(gain) occurring during the year	(0.2)	(0.3)
Currency exchange rate adjustment	(0.1)	(0.4)
Net adjustment to accumulated other comprehensive income	3.0	(4.8)
Accumulated other comprehensive income at end of plan year	7.2	4.2	$ 9.0
Net adjustment to accumulated other comprehensive income, income taxes	(1.9)	3.1
Amounts in accumulated other comprehensive income amortized and recognized as a component of net periodic benefit cost, net of income tax
Net loss / (gain)	3.3	(4.1)
Amortization of net (loss) gain	(0.2)	(0.3)
Total amortization expenses	3.1	$ (4.4)
Expected Benefit Payments
2022	4.0
2023	2.0
2024	2.3
2025	2.2
2026	2.5
2027 to 2031	17.4
Total	$ 30.4
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)	2.40%	1.90%	2.85%
Expected long-term rate of return on plan asset (as a percent)	3.00%	3.50%	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)	8.02%	7.43%	7.15%
Expected long-term rate of return on plan asset (as a percent)	8.02%	7.43%	7.15%
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	$ 1.6	$ 1.3	$ 0.9
Amortization of prior service cost / (credit)			(0.2)
Amortization of net loss/(gain)	0.2
Net periodic benefit cost	1.8	1.3	0.7
Change in benefit obligation:
Projected benefit obligation at beginning of year	23.8	20.6
Interest cost	1.6	1.3	0.9
Benefits paid	(1.4)	(1.5)
Actuarial (gain)/loss	(2.0)	4.5
Inflation adjustment	(0.6)	(1.1)
Projected benefit obligation at end of year	21.4	23.8	20.6
Change in plan assets:
Employer contributions		(0.1)
Benefits paid		(0.1)
Funded status at end of year	21.4	23.8
Amounts recognized in statement of financial position
Non-current liabilities	(21.4)	(23.8)
Total	(21.4)	(23.8)
Amounts recognized in accumulated other comprehensive income
Net loss (gain)	3.3	4.6
Total, net of tax	3.3	4.6	1.5
Net loss (gain), income taxes	(1.2)	(1.9)
Reconciliation of accumulated other comprehensive income:
Accumulated other comprehensive income at beginning of plan year	4.6	1.5
Net loss/(gain) amortized during the year	(0.1)
Net loss/(gain) occurring during the year	(1.1)	3.2
Currency exchange rate adjustment	(0.1)	(0.1)
Net adjustment to accumulated other comprehensive income	(1.3)	3.1
Accumulated other comprehensive income at end of plan year	3.3	4.6	$ 1.5
Net adjustment to accumulated other comprehensive income, income taxes	(1.2)	(1.2)
Amounts in accumulated other comprehensive income amortized and recognized as a component of net periodic benefit cost, net of income tax
Net loss / (gain)	(1.1)	3.2
Amortization of net (loss) gain	(0.1)
Total amortization expenses	(1.2)	$ 3.2
Expected Benefit Payments
2022	1.4
2023	1.4
2024	1.5
2025	1.5
2026	1.5
2027 to 2031	8.2
Total	$ 15.5
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)	2.40%	1.90%	2.85%
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	$ 1.6
Effect of one percentage-point decrease on total service and interest cost components	1.6
Effect of one percentage-point increase on post-retirement benefit obligation	19.9
Effect of one percentage-point decrease on post-retirement benefit obligation	$ 22.1
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)	8.02%	7.43%	7.15%