BENEFIT PLANS: (Details) $ in Millions	6 Months Ended
	Jun. 30, 2025 USD ($) plan	Jun. 30, 2024 USD ($)
Benefit plans
Number of noncontributory defined benefit pension plans | plan	2
Defined contribution plan and post-retirement defined benefit plans
Defined benefit plan, net periodic benefit costs
Service cost	$ 1.2	$ 1.3
Interest cost	1.9	2.0
Expected return on plan assets	(3.6)	(3.2)
Amortization of prior service cost/ (credit)	0.1	0.2
Amortization of net loss/(gain)	0.1
Net periodic (benefit) cost	(0.3)	0.3
Post-retirement health care plans
Defined benefit plan, net periodic benefit costs
Interest cost	1.0	1.1
Net periodic (benefit) cost	$ 1.0	$ 1.1