Basis of Presentation and Significant Accounting Policies - Calculation of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Basic:
Net income (loss)	$ (2.6)	$ 142.8	$ 133.3
Weighted average number of common shares during the period (in shares)	41,600,000	42,000,000.0	41,900,000
Net income per share - basic (in usd per share)	$ (0.06)	$ 3.40	$ 3.18
Diluted:
Weighted average number of common shares during the period (in shares)	41,600,000	42,000,000.0	41,900,000
Weighted average number of common equivalent shares to reflect the dilutive effect of common stock equivalent securities
CSUs related to deferred compensation for employees (in shares)	0	0	0
Total common and common equivalent shares adjusted to calculate diluted earnings per share (in shares)	41,800,000	42,200,000	42,000,000.0
Net income per share - diluted (in usd per share)	$ (0.06)	$ 3.39	$ 3.17
Equity Option
Weighted average number of common equivalent shares to reflect the dilutive effect of common stock equivalent securities
Stock options (in shares)	0	0	0
Restricted stock units
Weighted average number of common equivalent shares to reflect the dilutive effect of common stock equivalent securities
RSUs related to incentive compensation (in shares)	200,000	200,000	100,000