BENEFIT PLANS: (Details) $ in Millions	9 Months Ended
	Sep. 30, 2022 USD ($) plan	Sep. 30, 2021 USD ($)
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	$ 1.3	$ 1.1
Interest cost	1.7	1.2
Expected return on plan assets	(2.9)	(2.6)
Amortization of prior service cost / (credit)	0.1	0.1
Amortization of net loss (gain)	0.3	0.2
Net periodic benefit cost	0.5	0.0
Post-retirement Health care plans
Defined benefit plan, net periodic benefit costs
Interest cost	1.2	1.3
Amortization of net loss (gain)	0.1	0.1
Net periodic benefit cost	$ 1.3	$ 1.4