Earnings per Common Share Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Income (Loss) Available to Common Stockholders, Basic [Abstract]
Net income		$ 257.5	$ 202.2	$ 192.1
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Weighted average common shares outstanding for basic earnings per share computation		103,752,206	103,274,070	61,650,312
Dilutive effect of stock-based compensation (in shares)		27,897	66,929	91,516
Weighted average common shares outstanding for diluted earnings per common share computation		103,780,103	103,340,999	61,741,828
Restricted Stock [Member]
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)		119,144	52,027	83,952
Performance Shares
Weighted Average Number of Shares Outstanding, Basic and Diluted [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	470,622	908,476		333,767