Note 13 - Pension and Postretirement Benefits - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Plan and SERP Plan [Member]
Interest cost	$ 3.5	$ 4.4	$ 7.6	$ 8.7
Expected return on plan assets	(6.2)	(6.0)	(12.6)	(12.2)
Amortization of prior service cost	0.2	0.1	0.2	0.1
Amortization of net actuarial loss	0.8	1.2	1.7	2.7
Net periodic (benefit) cost	(1.7)	(0.3)	(3.1)	(0.7)
Employer contributions, net	0.2	0.3	0.4	1.3
Other Postretirement Benefits Plan [Member]
Interest cost	0.1	0.0	0.1	0.0
Expected return on plan assets	(0.1)	0.0	(0.1)	0.0
Amortization of prior service cost	0.0	0.0	0.0	0.0
Amortization of net actuarial loss	0.2	0.0	0.3	0.0
Net periodic (benefit) cost	0.2	0.0	0.3	0.0
Employer contributions, net	$ 0.3	$ 0.2	$ 0.5	$ 0.8