Note 4 - Shareholders' Equity (Details Textual) - USD ($)			1 Months Ended	3 Months Ended
	Mar. 05, 2024	Dec. 11, 2023	Feb. 28, 2021	Mar. 31, 2024	Mar. 01, 2024	Jan. 25, 2024
Parent Company [Member] | Two Thousand Twenty One Series A Zero Point Seven Five Percentage Remarketable Senior Notes [Member]
Debt Instrument, Face Amount			$ 1,000
Debt Instrument, Interest Rate, Stated Percentage			0.75%
Corporate Unit [Member] | Parent Company [Member]
Stock Issued During Period, Shares, New Issues (in shares)	2,745,733		3,500,000
Equity Units, Stated Value (in dollars per share)			$ 50
Percentage of Undivided Beneficial Ownership Interest			5.00%
Equity Units, Applicable Market Value (in dollars per share)					$ 58.6809
Equity Units, Number of Common Stock Obligated to be Purchased After Adjustment (in shares)					0.7845
Equity Stock Units Issued	$ 175,000,000
At The Market Program [Member]
Forward Sales Agreements, Shares Settled (in shares)		1,744,549		0
Proceeds from Shares Settled		$ 112,200,000
Sale of Stock, Maximum Aggregate Offering Price						$ 200,000,000
Forward Sales Agreements, Shares (in shares)				204,405
Forward Sales Agreements, Proceeds If Settled				$ 12,100,000