Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Restricted Shares
Beginning of period (in shares)	37,595	38,350
Issued (in shares)	10,405	10,895
Vested (in shares)	(13,475)	(11,650)
Forfeited (in shares)	0	0
End of period (in shares)	34,525	37,595
Unamortized Issue Date Fair Value
Beginning of period	$ 16.2	$ 15.5
Issued	18.3	16.0
Vested	0.0	0.0
Forfeited	0.0	0.0
Expense recognized	(3.2)	(3.2)
End of period	$ 31.3	$ 28.3