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
	Mar. 31, 2024	Mar. 31, 2023
Pension Plan and SERP Plan [Member]
Interest cost	$ 4.1	$ 4.3
Expected return on plan assets	(6.4)	(6.2)
Amortization of net actuarial loss	0.9	1.5
Net periodic (benefit) cost	(1.4)	(0.4)
Employer contributions, net	0.2	1.0
Other Postretirement Benefits Plan [Member]
Interest cost	0.0	0.0
Expected return on plan assets	0.0	0.0
Amortization of net actuarial loss	0.1	0.0
Net periodic (benefit) cost	0.1	0.0
Employer contributions, net	$ 0.2	$ 0.6