BENEFIT PLANS: (Details) $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($) plan	Jun. 30, 2021 USD ($)
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	$ 0.9	$ 0.7
Interest cost	1.1	0.7
Expected return on plan assets	(1.9)	(1.7)
Amortization of prior service cost / (credit)	0.1	0.1
Amortization of net loss (gain)	0.3	0.1
Net periodic benefit cost	0.5	(0.1)
Post-retirement Health care plans
Defined benefit plan, net periodic benefit costs
Interest cost	0.8	0.8
Amortization of net loss (gain)	0.1	0.1
Net periodic benefit cost	$ 0.9	$ 0.9