Earnings per Share and Stock Repurchase Program (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Jul. 31, 2023 USD ($)	Feb. 06, 2019 USD ($)
Common Stock
Common Stock conversion ratio, at the option of the holder	1
Net (loss) income
Net income | $	$ 291.2	$ 262.1	$ 251.5
Shares
Shares (in shares) | shares	33,500,000	33,400,000	33,500,000
Per Share Amount
Net income (in dollars per share) | $ / shares	$ 8.7	$ 7.85	$ 7.51
Dilutive securities, principally common stock options
Common stock equivalents (in shares) | shares		100,000	100,000
Common stock equivalents (in dollars per share) | $ / shares	$ (0.01)	$ (0.03)	$ (0.03)
Net (loss) income
Net income | $	$ 291.2	$ 262.1	$ 251.5
Weighted average number of shares:
Shares (in shares) | shares	33,500,000	33,500,000	33,600,000
Securities not included in the computation of diluted EPS
Net income (in dollars per share) | $ / shares	$ 8.69	$ 7.82	$ 7.48
Shares repurchased
Number of shares repurchased | shares	85,435	91,622	493,733
Cost of shares repurchased | $	$ 17.0	$ 16.0	$ 69.4
Class A
Common Stock
Common Stock, votes per share	1	1
Shares of Common Stock reserved for issuance under stock-based compensation plans | shares	1,775,014
Shares repurchased
Value of shares of the entity's Class A common stock authorized to be repurchased | $				$ 150.0	$ 150.0
Class B
Common Stock
Common Stock, votes per share	10	10
Shares of Common Stock reserved for conversion | shares	5,953,290
2019 stock repurchase program | Class A
Shares repurchased
Value of shares of the entity's Class A common stock authorized to be repurchased | $	$ 150.0
2023 repurchase program | Class A
Shares repurchased
Remaining authorized repurchase amount | $	$ 144.9