Note 13 - Pension and Postretirement Benefits - Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plan and SERP [Member]
Interest cost	$ 2.9	$ 3.4	$ 9.8	$ 11.8
Expected return on plan assets	(7.9)	(7.1)	(22.3)	(22.6)
Amortization of net actuarial loss	1.7	0.7	4.6	3.5
Net periodic (benefit) cost	(3.3)	(3.0)	(7.8)	(7.2)
Employer contributions, net	0.2	0.2	0.6	0.6
Amortization of prior service cost (credit)			0.1	0.1
Other Postretirement Benefits Plan [Member]
Interest cost	0.0	0.0	0.1	0.2
Expected return on plan assets	(0.1)	0.0	(0.2)	(0.1)
Amortization of net actuarial loss	0.1	0.1	0.3	0.3
Net periodic (benefit) cost	0.0	0.1	0.1	0.3
Employer contributions, net	$ 0.1	$ (0.1)	0.9	(0.4)
Amortization of prior service cost (credit)			$ (0.1)	$ (0.1)