Note 18 - Pension and Postretirement Benefits - Summary of Changes in Benefit Obligations and Plan Assets Amount Recognized (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair value of plan assets at January 1		$ 555.7
Fair value of plan assets at December 31		414.2	$ 555.7
Pension Plan and SERP Plan [Member]
Benefit obligation		431.7	459.9
Interest cost		14.7	11.0	$ 12.6
Actuarial gain		(86.6)	(9.0)
Plan participants’ contributions		0.0	0.0
Benefits paid		(28.9)	(30.2)
Benefit obligation		330.9	431.7	459.9
Accumulated benefit obligation at December 31		330.9	431.7
Fair value of plan assets at January 1		546.2	520.8
Actuarial (gain) loss		(111.8)	54.9
Employer contributions, net		0.8	0.7
Plan participants’ contributions		0.0	0.0
Benefits paid		(28.9)	(30.2)
Fair value of plan assets at December 31		406.3	546.2	520.8
Funded status at December 31		(75.4)	(114.5)
Pension assets, noncurrent (1)	[1]	(85.6)	(127.0)
Pension, SERP and postretirement benefits, current (2)	[2]	0.8	1.4
Pension, SERP and postretirement benefits, noncurrent (3)	[3]	9.4	11.1
Total Pension, SERP and Postretirement benefits		(75.4)	(114.5)
Other Postretirement Benefits Plan [Member]
Benefit obligation		6.0	7.5
Interest cost		0.1	0.1	0.2
Actuarial gain		(0.4)	(0.9)
Plan participants’ contributions		1.3	1.5
Benefits paid		(2.8)	(2.2)
Benefit obligation		4.2	6.0	7.5
Accumulated benefit obligation at December 31
Fair value of plan assets at January 1		9.5	10.5
Actuarial (gain) loss		(1.1)	(0.2)
Employer contributions, net		0.7	(0.1)
Plan participants’ contributions		1.3	1.5
Benefits paid		(2.8)	(2.2)
Fair value of plan assets at December 31		7.6	9.5	$ 10.5
Funded status at December 31		(3.4)	(3.5)
Pension assets, noncurrent (1)	[1]	(3.4)	(3.5)
Pension, SERP and postretirement benefits, current (2)	[2]	0.0	0.0
Pension, SERP and postretirement benefits, noncurrent (3)	[3]	0.0	0.0
Total Pension, SERP and Postretirement benefits		$ (3.4)	$ (3.5)

[1] Included in "Other noncurrent assets" in our accompanying consolidated balance sheets

[2] Included in "Accounts payable and accrued liabilities" in our accompanying consolidated balance sheets

[3] Included in "Other noncurrent liabilities" in our accompanying consolidated balance sheets